Bio6.Blueprint of Life

keep it simple science TM

www.keepitsimplescience.com.auHSC Biology Topic 2copyright © 2005-2007 keep it simple science

Baulkham Hills High School SL#802445

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but first, an introduction...

HSC Biology Topic 2

BLUEPRINT of LIFEWhat is this topic about?To keep it as simple as possible, (K.I.S.S.) this topic involves the study of:1. EVOLUTION

2. MENDELIAN GENETICS3. CHROMOSOMES & DNA STRUCTURE

4. MOLECULAR GENETICS & MUTATION5. REPRODUCTIVE TECHNOLOGIES &

GENETIC DIVERSITY

EvolutionIn earlier topics you have already been introduced tothe concept of Biological Evolution, and themechanism of “Natural Selection”. Now you willstudy in more detail the evidence for evolution andTheory of Evolution.

GeneticsThe science of inheritance was discovered about150 years ago by a monk living in an obscuremonastery in central Europe. In this topic you willstudy the simple patterns of inheritance that hediscovered.

Gregor Mendel (1822-1884) experimented withgarden peas for 12 years. You will study his resultsand the reasons for his success as an experimenter.

Chromosomes & DNAYou will next move on to study things that Darwin &Mendel would have been delighted to have known...the cellular and molecular basis of Genetics andEvolution. You will see the link between inheritance,cell division, chromosomes and the basis of it all...the DNA molecule and the Genetic Code.

In the section on Molecular Genetics you willlearn how the DNA acts to control all thecharacteristics of each organism (the “phenotype”)and how Mutations can occur to alter the code andproduce new characteristics for evolution to work on.

In the final section you will look briefly at wheremodern Biology is heading into ReproductiveTechnologies and Genetic Engineering. (This controversial area can be studied morethoroughly in one of the later Option topics)

SimulatedPhotograph ofHumanChromosomes

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AA sseeccttiioonn ooff DDNNAA ccaarrrriieessaa ccooddee ttoo ssppeecciiffyy oonnee

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Photo: Sasan Saidi




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CONCEPT DIAGRAM (“Mind Map”) OF TOPICSome students find that memorizing the OUTLINE of a topic helps them learn and remember the concepts andimportant facts. As you proceed through the topic, come back to this page regularly to see how each bit fits thewhole. At the end of the notes you will find a blank version of this “Mind Map” to practise on.

Non-MendelianInheritance.Sex-linkage

& Codominance

Meiosis &gamete

formation

DNAReplication

Mendel’sexperiments,

and the reasonsfor his sucess

•Palaeontology•Biogeography•Comparative

Embryology•Comparative

Anatomy• Biochemistry

Divergent &

ConvergentEvolution

NaturalSelection,Survival ofthe Fittest

His results andexplanations

Alleles & genes.Homozygous,heterozygous.Genotypes &phenotypes

PedigreesFamily trees

Punnettsquares

DNAstructure

Some historyof our

understanding

The link toevolution

The link tophenotypes

Artificialinsemination and

pollination.Cloning

PunctuatedEquilibrium

Effects on geneticdiversity

GeneticEngineering and

“Transgenicspecies”

Sources ofvariation

THE BLUEPRINTOF

LIFE

Chromosomes &

DNA

MendelianGenetics

Molecular Genetics&

Mutations

ReproductiveTechnologies

& Genetic Diversity

Evolution

The EVIDENCEfor Evolution

The THEORY ofEVOLUTION

Chromosomes,genes

& DNA

Mutation&

mutagens

DNATranscription &

Translation

Dominant-Recessiveinheritance.

Monohybrid crosses




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The Evidence for EvolutionThere is overwhelming evidence that life on Earth hasundergone a sequence of changes over the past 3.5 billionyears or so. Here, briefly (K.I.S.S. Principle) are the mainsources of that evidence:

Palaeontology The Study of Fossils The fossil evidence is undoubtably our most important,direct evidence showing that life on Earth has changed.

The fossils not only show that life was once different, butthat the changes follow a pattern or sequence...

...this is evolution.

How do we know this to be fact? Not only do we havemany fossils of extinct organisms, but we can place themin time sequence to see the patterns.

Initially, scientists could only place fossils in relative timeorder by correlating the sequences, as suggested in thediagram above.

Now we can also place absolute times on many fossils by“Radiometric Dating”... the determination of the actualage of things by measuring the residual radioactivity ofcertain, naturally-occurring radio-isotopes in the rocks.(To revise this more thoroughly, see Preliminary Topic 3“Life on Earth” page 4)

Fossils of “Transitional Forms”Only a tiny fraction of all the zillions of organisms thathave ever lived have ended up being fossilized. The fossilrecord is, therefore, incomplete and a rather patchy recordof evolution.

Despite this “patchiness”, there are some fossils that havegiven us a glimpse of the change that occurred when onetype of life was evolving into another. Such fossils arecalled “Transitional Forms”

Perhaps the most famous is Archaeopteryx.(“Archae”= ancient, “pteryx”= wing)When this fossil was first discovered, its skeleton wasclearly that of a small dinosaur. Only later was it noticedthat the faint outlines around the fossil were theimpressions of feathers. This was a dinosaur-bird!

Transitional fossils are important evidence that each newtype of life that “appears” in the fossil record did in factevolve from a previous ancestor. Scientists have discoveredtransitional fossils showing:

• reptiles evolving to become mammals• ferns evolving to become cone-bearing plants• lobe-finned fish evolving to become amphibians

...and many more, including fossils of our ownprobable ancestors, who were very ape-like, butundoubtably human-like too!

1. EVOLUTION

Sediments are laid down on top of the previouslayer, so the lower layers are older.

Rocks and fossils llooccaattiioonn 11

Rocks and fossils llooccaattiioonn 22

foss

ils co

rrelat

e

from

one

plac

e

to an

othe

r

youngestfossil

Oldestfossil

ANCIENT TIMES MODERN TIMES

Less complexity More complex typesLess variety Greater varietyLess like More and more

present-day life resembling modern life

Clawed wings

Bony jawwith teeth

Bony tailcovered infeathers

It is very unlikelythat Archaeopteryx

could fly like amodern bird. It mayhave climbed trees &

glided down oninsect & lizard prey

Reconstruction of Archaeopteryx

HSC Biology Topic 2copyright © 2005-2007 keep it simple science


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Biogeography (the study of how life is distributed)When Charles Darwin travelled around the world on boardHMS Beagle in the 1830’s, it was the distribution of differenttypes of life in different places that first gave him the ideafor Evolution.

He noticed that each continent had its own characteristicbiota, often showing similar features although often notclosely related to each other. For example, each continenthas characteristic grazing mammals:

All these animals are relatively large, fast-running, with flatgrinding teeth, and all lead pretty much the same lifestyle.So why is there not just one type of large grazer in theworld, living on every continent?

Evolution explains why. On each separate continentdifferent animals have evolved to fill the “large grazingherbivore” role, often beginning that evolution from anancestor quite different to that on other continents.

Another aspect of Biogeography was seen by Darwin on amuch smaller scale in the Galapagos Islands. He discoveredthat the islands were populated by many different species ofsmall birds... finches. Although all were obviously related toeach other, each separate island had its own particular species.

Why?The explanation is:• the islands were first colonized by one type of finch,

which spread to all of the islands in the group.• on each separate island conditions were different

(eg different foods available) so each population evolvedin a different way, into a different species.

Comparative EmbryologyIf the embryos of various vertebrate animals are compared,it is found that they are remarkably similar, even thoughthey later develop into quite different animals.

Why should they be so similar when they grow up to bevery different animals? Why should (for example) a humanembryo have a tail and gill arches like a fish?

Comparative AnatomyWhen the body structures of different organisms arecompared, it is often obvious that they share commonfeatures, even though those body parts might be used indifferent ways.

The classic example of this is the Pentadactyl Limbstructure of the vertebrate animals.

Each limb is used in very different ways by animals thathave very different lifestyles, yet all have exactly the samebasic arrangement of bones. Why?

Once again, these are FACTS that are consistent with, andeasily explained by, the concept of EVOLUTION.

www.keepitsimplescience.com.au


AAffrriiccaannAAnntteellooppee

SthAmericanLlama

OZRoo

BIOGEOGRAPHY doesn’t prove Evolution hasoccurred, but many facts about the distributionof organisms are best explained by Evolution

Ancestral Finch

Island 1Island 2 Island 3

Some Vertebrate Embryos...

...andwhat they develop into

Evolution explains this as the result of all theseanimals evolving from a common ancestor

which had an embryo like this.

Some Vertebrate Forelimbs (Arms)(Not to same scale)

1 bone inupper arm

2 bones inforearm

5 digitsHumanArm

WhaleFlipper Bat

Wing

CatLeg

LizardLeg

Evolution explains this as the result of all theseanimals evolving from a common ancestor

which had this bone structure.

(“Pe

nta”

= 5

,“da

ctyl”

=fin

gers

)

Steve Clayton

Luis Rock

North American Bison

Photos: Diana




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BiochemistryAll the life-forms on Earth have remarkable similarities atthe molecular level. All organisms have basically the same:

• genetic code in their DNA• enzymes used for basic metabolic processes, such as

cellular respiration• structural chemicals in their basic cell components,

such as the phospholipids in cell membranes.

Selective Breeding Humans have “domesticated” many plants and animalssuch as cattle, sheep, chickens, dogs, rice, wheat, tomatoes,and so on. Over thousands of years, human farmers andbreeders have had control over the breeding of theseorganisms. Often a farmer or animal keeper will choosevery carefully which individuals will be allowed to breed,always selecting the best ram to breed with the ewes, orseeds from the best plants to sow for next year’s crop.

The result is that these species have changed.

All varieties of domestic dog, for example, belong to thesame species, and all are believed to be descended from thewolf which may have been domesticated as the first“puppy” about 12,000-15,000 years ago.

WHY SHOULD ALL ORGANISMSHAVE THE SAME STRUCTURESAND CODES IN THEIRDNA?

Once again, this doesn’t prove that evolutionoccurred, but it is consistent with the idea that

life on Earth has evolved from common ancestorswho had these biochemical features.

Selective Breeding proves that a species can be changed.

Humans can do it artificially,in the wild it happens by “Natural Selection”

The preceeding pageshave outlined the facts &

evidence for what hashappened.

Next we look at the how & why...

The Theory of Evolution,by “Natural Selection”

How New Technologies are Changing OurIdeas About Evolutionary Relationships

The new technology of analysing the sequence of DNAmolecules is changing our ideas about the evolutionaryrelationships between living things.

For example, the evolutionary relationship between LIZARDS, CROCODILES and BIRDS.

Traditionally crocodiles & lizards are classified as “Reptiles”and considered a separate class to the “Birds”. It was alwaysthought that the lizards and crocodiles were closer in anevolutionary sense, and shared a common ancestor closertogether than either was to the birds.

This relationship has been overturned by DNA analysis.

DNA sequencing shows that birds and crocodiles are moreclosely related to each other than either is to the lizards.

Stand by for more revelations as DNA analysis reveals more!

Side

-ttra

ck

CLOSELYRELATED More

Distant

More Distant

Based on structuralsimilarities & differences

Based on DNA analysis

CLOSELY RELATED

Photos byDiana

“SPIKE”



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Darwin & WallaceIn the 1830’s a young naturalist, Charles Darwin (1809-1882),voyaged around the world on the naval survey ship HMSBeagle. He became convinced that living things had changed,and spent the next 20 years researching, gathering evidenceand developing the “how” of a theory to explain evolution.

Meanwhile, another Englishman, Alfred Wallace (1823-1913) came up with exactly the same idea after his journeysin the 1840’s and 1850’s. We often give Darwin most of thecredit for this major scientific theory, but Wallace’scontribution should not be forgotten.

In 1859 they jointly published an outline of their theory,and Darwin followed up with his detailed book “Origin ofSpecies” about 2 years later.

The Darwin-Wallace Theory of EvolutionYou need to learn the details of this theory. This is bestdone as a series of numbered points:-

1. All organisms produce more offspring than can survive.Plants scatter thousands of seeds and maybe only one evermakes it to plant maturity. Oysters produce a million eggsat a time, but only 1 or 2 survive. In all species, the breedingrate is higher than the survival rate.

2. In every species there is variation among the individuals.Each animal or plant is slightly different to the othermembers of the species. The differences may be slight, andmight not be easily visible, but they’re important!

If you put points 1 & 2 together, you can see that survivalis uncertain, AND the chances of survival are not equal foreach individual.

3. Nature selects which individuals survive.This is called “Natural Selection”, and it is explained inmore detail soon.

4. Those best suited to their environment survive, andreproduce, and pass on their characteristics to theiroffspring. This is called “Survival of the Fittest”, and itwill be discussed in more detail later.

5. Over generations, the species changes (Evolves) as eachgeneration is slightly different than before, because onlysome, selected individuals have bred and passed on theircharacteristics.

More on “Natural Selection”The following is revision material from Preliminary Topic 4and needs to be understood...

“Natural Selection” refers to the way that the conditions of natureconstantly select who survives and who dies. If survival depends onspeed to run from a predator, then the faster individuals survive andthe slower ones get eaten. In a drought those plants with slightlythicker cuticle on their leaves conserve water and survive, whileothers die.

Any characteristic might be a help to survive under differentconditions...• a better immune system helps, when diseases strike...• more inquisitive behaviour might find more food...• more timid behaviour might avoid dangers...• brighter coloured flowers might attract pollinators...• larger body size might deter predators...• smaller body size might allow more food gathering on the

ends of small branches of trees.

It is difficult to predict exactly which characteristic, or combinationof characteristics, might help survival... it depends on what happensin the environment:

The species has changed... it has evolved by adapting to changes inits environment.

It may seem as if “Evolution” is an intelligent force which directsorganisms in a an appropriate direction. In our fictitious populationof animals, the climate became colder and it would seem that someevolutionary force caused an appropriate change in the population...they became squat & hairy to conserve body heat better.

But of course “squat” and “hairy” were already in the population.Their type simply became more common, and finally predominant,because they survived in greater numbers and reproduced to pass ontheir characteristics to their offspring.

Evolution is not intelligent. Nature selects the survivors from thedifferent “types” available. Survivors breed... if you’re dead, youcan’t reproduce!



HOW NATURAL SELECTION WORKS

A population of a species with a lot of “variations”

hairy long legs big earslong neck dark colour squat body

TThheenn,, tthhee cclliimmaattee cchhaannggeess......wwiinntteerrss ggeett ccoollddeerr

hairy survives Squat survives

Survivors breed

Many die in the harsh winters

The survivorspass on theircharacteristics.Over generationsmost of thepopulationbecome squatand hairy.



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More on “Survival of the Fittest”“Survival” does not just mean survival. The biggesttoughest animal in the herd, who scares predators away,gets to eat most of the food and lives to a ripe old age, is acomplete failure if it does not reproduce!

In evolutionary terms “Survival” means to survive andreproduce. Reproduction is the true measure of “survival”.An animal which does not live long, but manages toproduce many, viable offspring is an evolutionary success!

“Fittest” refers to those individuals with a combination ofcharacteristics best suited to their environment. It doesn’tnecessarily mean biggest, fastest, strongest... those bestsuited to some environments might be the smallest,sneakiest, most cautious types.

The Importance of VariationIt is vital for the on-going survival of a species that it hasvariation among the individuals of the population.

When changes occur in the environment, a species with alot of variation has more chance to survive, because out ofall the different “types” there is a good chance that at leastsome will survive to breed and continue the species.

A species with little variation within it, might have nosurvivors from an environmental change, and becomeextinct.

What constitutes an environmental change? It could be...• a change of climate• a new disease, predator or competitor in the ecosystem• a change in availability of a food resource

...or any other biotic or abiotic factor.

Effects of Changing ConditionsEnvironments can change in many different ways. Forexample, we know that ice-ages come and go, and climateschange as the continents gradually “drift” to new locations.Any change in an environment will result in NaturalSelection picking out different characteristics for survivaland the species will evolve in line with the environmentalchange (OR, if the change is sudden and drastic, there willbe fewer survivors every generation and the species willdecline into extinction!)

The following case studies serve to make this point, and arealso examples of observed “micro-evolution” providingfurther evidence that Evolution by Natural Selection canand does occur.

A Change in the Physical EnvironmentA classic example is the change in the population of theEnglish Pepper Moth which has been studied anddocumented over the past few hundred years.

This moth always rests during the day on tree trunks, whichin natural forests, are mostly covered in motley-patternedlichens. Under these conditions the light “peppery” mothsare the most common form, although occasional blackmoths occur.

During the coal-burning phase of the Industrial Revolutionmany forests were damaged by pollution. The lichens werekilled and tree trunks blackened with soot.

It was observed that the Pepper Moth population changedin the proportion of peppery to black types.

Now that industrial pollution has been stopped, the mothshave evolved back to being mostly of the peppery type.



... or the most charmingand socially acceptable

In unpolluted forests,the lighter-colouredmoths are camouflaged

In polluted forests, theblack moths arecamouflaged

Predators spot the blackmoths more easily

Predators spot the lightmoths more easily

Lighter-colouredmoths survive andbreed in greaternumbers

Black moths surviveand breed in greaternumbers

Population ratio

Population ratio

Light m

oths are “fittest”

Black

mot

hs ar

e “fit

test”



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A Change in the Chemical Conditions of the Environment

Another example of “micro-evolution” was observed whenDDT insecticide began to be used against a variety of insects,such as disease-carrying mosquitoes or crop-eating pests.

Initially, the chemical was a huge success, decimating theinsect populations. But then Natural Selection did itsthing...

Among the millions of insects in each population there wasvariation. A few individuals had a natural resistance to theDDT and they survived and reproduced and passed ontheir resistance to their offspring. Over many generationsthe non-resistant types were killed, and resistant types keptsurviving and breeding until almost the entire populationwas resistant. DDT was no longer useful for killing insects.(Just as well too, because it was later discovered to havesome negative environmental impacts on other species)

The DDT in the chemical environment acted as a“Selecting Agent” resulting in the evolution of the insectsby natural selection and survival of the fittest.

Competition for ResourcesIn a previous topic it was pointed out that competitionbetween 2 species for the same resources usually results ina “winner” and a “loser”... the loser becoming extinct, atleast within the area of competition.

However, this is not the only possible outcome. If amongthe natural variations within either species there are someindividuals who are perhaps less fussy about their food ornesting sites (what ever the resource might be) and who cansurvive on slightly different foods, or utilize differentnesting sites, then they will have an advantage to survive.

Survivors breed and pass on their characteristics. Overgenerations the species evolves to be using a slightlydifferent resource. Therefore, it is no longer in competitionand both species can survive... a “Win-Win” situation.

This outcome is called “Resource Partitioning” and iscommonly observed in nature. For example, the manygrazing species of the African plains avoid competitionbecause each has slightly different plant preferences amongthe various grasses, shrubs, etc.

Divergent Evolution (“Diverge” = move apart)One of the aspects of evolution to be aware of is theimportance of Isolation.

Rember Darwin’s finches on the Galapagos Islands?

From one ancestral species of finch over a dozen differentspecies evolved, one on each of the islands in the group.The key to this “Adaptive Radiation” is the fact that once apopulation of finches colonized a new island they wereisolated from other populations. Movement of birdsbetween islands must have been a rare event, and eachpopulation was effectively cut off from other populations.

On each island conditions were different... different foodswere available, different conditions of water supply, shelter,nesting sites, predators and so on. Natural selection causedeach population to evolve along a different path until theybecame different species... they had diverged!

Now, even if they mixed together again, they could notinterbreed because their mating rituals, sperm & egg cellsand DNA have changed to become incompatible. They areforever separate. This is how we think all species havearisen from common ancestors over millions of years.

Convergent Evolution (“Converge”=come together)If totally different organisms live in the same kind ofenvironment and lead similar lifestyles they will be subject tothe same sorts of “Selection Pressures” and evolve many ofthe same features, so they may come to resemble each othereven though not closely related at all.

A classic example is the shark (a fish), dolphin (a mammal)and the extinct ichthyosaurus (a reptile)

All 3 animals are (were)fast-swimming fish-hunters of the ocean. All evolved the same streamlinedshape, powerful tail, dorsal fin and sharp teeth to suit thislifestyle. The resemblance is superficial, and they are verydifferent in the details of body structure and metabolism.For example, the shark is a gill-breathing ectotherm, whilethe dolphin is a lung-breathing endotherm.There are many other examples of such convergence.



New competitorenters ecosystem

LOSER

WINNERSpecies using resource.Population stable

Ancestral Finch

Island 1Island 2 Island 3

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Worksheet 1Fill in the blanks. Check your answers at the back.

Part A Evidence of EvolutionThe most important, direct evidence for Evolution comesfrom a)....................................................., the study ofb)..................................... This shows that life on Earth haschanged from being c)........................... complex to becomed).............................. complex, and showing e).....................variety to f)............................... variety and becoming moreand more like g).......................................................... over aperiod of h)......................................... of years. Initiallyscientists could only place fossils in i).....................................time order by j).......................................... the fossils from oneplace to another. The technique ofk)........................................ dating has allowed absolute agesto be measured.

An important type of fossil is a l)............................................form, which is an “in-between” organism. A good exampleis m)........................................................ which lived about 100MYA. It appears to be a n)......................................................in the process of evolving into a o).......................................

Biogeography is the study of p)............................................................ It gives indirect evidence for evolutionbecause the distribution of species can be best explained byevolution.

Comparative Embryology reveals that vertebrate embryosare all q)......................................................... to each other,even though each animal grows up to ber).................................................... This is explained byevolution as being due to these animals all evolving from as)..............................................................................

Similarly, the study of Comparative Anatomy shows muchthe same. For example, the forelimbs of vertebrates havethe same t).................................................................... eventhough each animal uses the limbu).........................................................................................This “5-digit” limb structure is calledv)................................................................

Biochemistry reveals that all organisms have the samegenetic code in their w)......................... and use the samex).................................... to control their metabolic processes.This is evidence of y).....................................................................................................

Selective Breeding of domesticated plants and animalsshows that z)................................................................................

Part B The Theory of Evolution

The Theory of Evolution was developed independently bya)........................................... and .................................................It can be summarized in 5 main points:1. All organisms produce b)........................................................2. Every species shows c)...........................................................3. d)”............................................................” occurs to choosethe survivors.4. Those organisms e).................................................... to theenvironment survive and f)........................................................This is called g)”.........................................................................”5. Over generations, the species h)............................................because the selected characteristics are being passed on ingreater proportions.

“Natural Selection” refers to the way that the forces ofnature choose who survives. These “forces of nature”could include disease, i)............................... and......................................., and any factors in the environment.“Survival of the Fittest” refers to how the organismsj).............................................................. to the environmentwill survive and k)..........................................................Variation within a population is vital so that if theenvironment changes, there are more likely to be someindividuals who will l).................................................. andm)..................................................

Changes to actual populations have been observed.The n)............................. Moth of England was observed toundergo a population change over generations due too)..................................... pollution changing the backgroundcolours of its environment. This led to a change in the ratioof p).....................................................................................Another example was due to a chemical change in theenvironment. When the insecticide q)....................... waswidely used it acted as a r)”..............................................agent”, causing mant pest species to evolve to becomes).................................................................

Competition for resources can result in one species losingand becoming t).................................. However, anotherpossible outcome is called “Resourceu).............................................” which results if one speciesevolves to avoid the competition byv)...................................................................................................

“Divergent Evolution” is when one speciesw)....................................... into ...........................................This happens when different populations of a speciesbecome x).............................................. from each other. Eachpopulation is subject to different y)..........................................pressure due to the differing environments.

“z).....................................Evolution” is when quite unrelatedspecies evolve to aa)........................................... each other.This can happen because they live in ab)..................................environments and so natural selection favours evolution ofsimilar ac)............................................. A good example is theshark and ad)............................................ which have manycommon ae)................................................ even though theyare not af)................................................. to each other.

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HSC Biology Topic 2copyright © 2005-2007 keep it simple science www.keepitsimplescience.com.au


WHEN COMPLETED, WORKSHEETS BECOME SECTION SUMMARIES




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In Charles Darwin’s lifetime there were 2 parts of hisTheory of Evolution that no-one could explain.Where Does Variation in a Species Come From?

(That will be explained later in this topic)How Are Characteristics Passed On to Offspring?

... that will be explained right now!

The Experiments of Gregor MendelMendel was the Abbot of a monastery in what today is theCzech Republic. He was trained as a teacher and was not aprofessional scientist, but became interested in discoveringhow inheritance works. The monks grew most of their ownfood, so Mendel worked his investigations into the day-to-day vegetable gardening by choosing to experiment withgarden peas.

First he bred his pea plants over several generations toselect plants that were “pure breeding” for certaincontrasting characteristics, such as...

Each type was “pure breeding”, meaning that if they wereself-pollinated they always produced offspring of exactlythe same type as themselves.

Then he cross-pollinated 2 contrasting types to obtain“hybrid” (cross-breed) offspring. The result was that all theoffspring showed the characteristic of one parent and nonetook after the other. For example:

Next, he self-pollinated the plants of the F1.

Mendel didn’t do this with one or two plants, but withmany. His 2nd generation groups of offspring totalledthousands of plants, not just a few.

He got the same result with flower colours, seed shapes,seed pod colours, and so on. In every case the firstgeneration always took after one parent completely, and thesecond generation always appeared (in their thousands) in aratio of very close to 3:1.

Mendel’s Explanation of the Results (Using Modern Terminology)

• Each characteristic is produced by “factors” (we now callthem genes) carried by the plants. For example, there is agene for tallness of stem, and a corresponding gene fordwarf stem. There is a gene for purple flower and anotherfor white flowers, and so on for other characteristics.

The genes which control “opposite” forms of the samecharacteristic are called “alleles”, or “allelic genes”.So the genes for “tall” and “dwarf ” are alleles.Genes for “purple flower” and “white flower” are alleles.

• One of the alleles is “Dominant” over the other, whichis said to be “Recessive”. We usually use letters of thealphabet to designate this:

Tall ( T ) is dominant to Dwarf ( t ) Purple flower ( P ) is dominant to white ( p )

• Each plant carries 2 genes for a characteristic. The 2 genesmay be the same as each other (“homozygous”) ordifferent to each other (“heterozygous”).

Example: for the height characteristic, the possibilities are:TT = homozygous, Tall plantTt = heterozygous, Tall plant, because T dominanttt = homozygous, Dwarf plant (cont...)

2. MENDELIAN GENETICS

TALL v DWARF PURPLE v WHITEFLOWER FLOWER

XTTAALLLL FF1 ppllaanntt

F22 (2nd Generation) Offspringoccurred in a ratio of 3:1

X“X” is short-handfor “crossed with”

TTAALLLL DDWWAARRFF

F11 (1st Generation) Offspring were ALL TALL

Mendel explained this result by suggesting that the“factor” (GENE) which caused “Tallness” was

DOMINANT to the gene for “Dwarfism”.Dwarf is RECESSIVE to Tall.

SSEELLFF



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Mendel’s Explanation of the Results (...continued)• Although each plant carries 2 genes for eachcharacteristic, only one gene is passed into the gametes(pollen or ovules). Each parent passes on one gene, so theoffspring gets one from each parent and gets back tohaving 2 genes for the characteristic.

Which one is passed on is completely at random.

Now, we re-examine Mendel’s experiment using symbols totrace the genes through the generations:

This explains why Mendel observed a ratio of about 3:1 inthe plants of his F2 offspring.

Note that his experimental ratios were approximately 3:1,but not exactly 3:1. This is because the actual combinationsof gametes at fertilization occur at random. He bred largenumbers of plants and so his actual ratio was very close totheoretical.

Reasons for Mendel’s SuccessGregor Mendel had discovered the basic mechanism ofinheritance. Scientists before him had studiedinheritance, but had failed to discover the simplepatterns. Why was he successful?

• He chose simple, easily-identified characteristics whichoccurred in just 2 forms...e.g., height; either tall or dwarf

• He began with “pure-breeding” parent plants

• He bred large numbers of plants so that the numbersof offspring were statistically significant.(If he’d produced just a few offspring then randomchance could have produced confusing results)

Reasons for Mendel’s Work Being IgnoredMendel published his results in 1865 in a German naturalscience journal and received instant oblivion. Why?

• He was not a recognised scientist, and had no contactwith the “scientific establishment” of his time. His work was read by only a small circle of people, who failed to see its significance.

• His work was written only in German, while all the “important” science of that time was appearing in English or French, in well-known journals in England,France & USA.

It was not until well after Mendel’s death that in 1900 hiswork was “discovered” by scientists, and his greatcontribution was recognised. He is now known as the“Father of Genetics”.



These are “Phenotypes”...descriptions of the outward

appearance

These are“Genotypes”the actual

genespresent

Only 1gene ispassedintogametes

GAMETES

PossibleGAMETES

PARENT PLANTS Tall x Dwarf

TT tt

Tall x TallTt Tt

T

TtTall

t

FertilizationAll the F1offspringreceive thiscombinationof genes

Mendel’s “Pure-Breeding”parent plants were

homozygous for eachtrait... 2 genes the same

Self-pollinatingthe F1 plants is

the same ascrossing with

the samegenotype

ALL THE F1OFFSPRING ARETALL, BUTHETEROZYGOUS

T Tt t

TT Tt Tt ttTALL TALL TALL DWARF

Ratio of Phenotypes 3 Tall : 1 Dwarf

Next, the F1 plants were self-pollinated to produce the F2

possiblefertilizations

The Punnett SquareThe “working out” of the cross as shown at the left can bea bit messy and confusing. A scientist called Punnettinvented a simpler method which you must learn to use.

The “Punnett Square” working below shows the samecross... the formation of the F2 plants in Mendel’sexperiment.

Tt Tt

T & t T & t

T t

T

t Tt

TT

tt

Tt

xGGeennoottyyppeess ooffppaarreennttss

gametesLLiisstt ooff aallllppoossssiibblleeggaammeetteess

PPuunnnneetttt SSqquuaarreettaabbllee sshhoowwss aalllltthhee ppoossssiibblleeooffffsspprriinnggggeennoottyyppeess

TThhee pphheennoottyyppeessooff ooffffsspprriinngg aarreewwrriitttteenn aass aa rraattiioooorr ppeerrcceennttaaggee

PPhheennoottyyppeess ooff OOffffsspprriinnggTTaallll :: DDwwaarrff

33 :: 117755%% :: 2255%%



12

Monohybrid Crosses“mono” = 1 (referring to just one characteristic)“hybrid” = cross-breed, when 2 “types” are crossed

It has been found that there are many characteristics, in allsexually-reproducing organisms, which are inherited justthe way Mendel discovered...these are cases of “Mendelian Genetics” and you need tobe able to predict the outcomes of simple crosses.

Study the following examples to help you work through thenext worksheet.

Sample Problem 1In mice, black coat (B) is dominant to albino (b).Predict the outcome of mating a heterozygous blackmouse with an albino.

Solution

Parents are

Sample Problem 2In drosophila fruit flies, the allele for long wings (L) isdominant to the allele for short wings ( l ). A pure breedinglong winged fly was crossed with a short winged fly. Theiroffspring were allowed to mate among themselves toproduce a second generation. There were 240 flies in theF2. Predict how many of each phenotype would occur.

SolutionTo work out the F1, a punnett square is not really needed.

Parents genotypes LL x ll

Gametes possible L only and l only

All the F1 flies must be Genotype: LlPhenotype: 100% Long winged

Then, for the F2:

If the F2 comprises 240 flies, we should expect close to:

180 long wing flies and 60 short wing flies

(However, this is a statistical prediction only, and we shouldnot be surprised if the actual numbers were (say) 190 to 50.)



Bb bb

B & b b & b

b b

B

b bb

Bb

bb

Bb

x

gametes

PPhheennoottyyppeess ooff OOffffsspprriinnggBBllaacckk :: AAllbbiinnoo

11 :: 115500%% :: 5500%%

Ll Ll

L & l L & l

L l

L

l Ll

LL

ll

Ll

x

gametes

PPhheennoottyyppeess ooff OOffffsspprriinnggLLoonngg WWiinngg :: SShhoorrtt WWiinngg

33 :: 117755%% :: 2255%%

You will soon come to realize that only 3 outcomes are possible:

100% : zero 50% : 50%75% : 25%

NOW TRY THE PROBLEMS IN WORKSHEET 2



Pedigrees (Family Trees)Another skill you must learn is how to read, interpret andconstruct a pedigree diagram.

This is a diagram showing the inheritance of a trait througha family. It is used particularly with human families to tracesome characteristic over a number of generations.

Symbols Used in Pedigree Diagrams

Malewith trait being studied

Female with trait

Horizontal connections are “marriage lines”.Vertical lines lead to children of that couple.Each generation is numbered by Roman Numerals.Individuals may be numbered for identification

ExampleIn humans, some people can “roll their tongue” whileothers cannot. This is passed on by simple MendelianInheritance. Here is a pedigree of a family showing howthis trait was passed on.



13

InterpretationIn Generation I, individuals 1&2 were both tongue-rollers.They had 4 children, a daughter and 3 sons. Most of thekids can roll their tongues, but son “4” cannot.

This means the inability to tongue roll must be recessive.(Whenever a child shows a trait different to both parents,the child’s phenotype must be recessive.)

Therefore, tongue-rolling ability must be dominant.

We can now assign symbols... tongue-rolling (R)non rolling ( r )

...and work out most people’s genotypes:1 2 3 4 5 6 7 8 9

Rr Rr ? rr ? Rr rr rr rr

(Individuals “3” & “5” might be either “RR” or “Rr”.... more information needed to be sure which)

Questions & AnswersHow can we be sure that parents 1 & 2 are both “Rr”(heterozygous)?A: Since they produced son “4” who is a non-roller (andhas to be genotype “rr”) both 1 and 2 must be carrying therecessive gene. Therefore, both must be “Rr”.

Can we be sure that son “6” is “Rr” and NOT “RR”?A: He married a non-roller (rr) and both the children ingeneration III are non-rollers. Therefore, son “6” musthave passed on a recessive gene to his children. He must beheterozygous (Rr) to do this.

If “6” and “7” had another child, could it be a tongueroller? What’s the chance?A: Yes. The cross is Rr x rr.If you work out a punnett sqare for this, you will see thatthe expected outcome is 50% rollers and 50% non-rollers.The chance for the next child is 50% either way, and isNOT affected by the fact they have already had 2 non-roller children.

Male without trait

Female without trait

11

55

22

33 44 66 77

88 99

I

II

III

GGeenneerraattiioonnss

TRY THE PROBLEMS IN WORKSHEET 2

Uses of Pedigree DiagramsPedigree diagrams are used to study humaninheritance because it is not moral or ethical to carryout breeding experiments on people to discoverwhich traits are dominant/recessive.

Some human disorders are inherited. Examples arehaemophilia (in which blood will not clot properly)and colour-blindness (inability to distinguish certaincolours). Health professionals can study affectedfamilies by compiling a pedigree chart, then advisepeople about the risks to future children. Thisallows people to make informed decisions aboutfamily planning.

Sarah can...

Nathan can’t



Worksheet 2When Complete, Use as a Section SummaryPart A Fill in the blanksGregor a)............................... was a monk who experimentedwith b)..................... plants and discovered the basics of howcharacteristics are c)................................................ He startedwith plants that were d)......................-breeding for 2opposing traits, and crossed them. For example, he crossedpure-breeding tall-stem plants with e)......................................,f)..........................-stem plants. In the first generation, org)............., the offspring plants were 100%h)..................................... When these were allowed toi).........................-pollinate, the F2 (which means j)................................................................) showed a ratio ofk)....................... of tall to dwarf plants.

He explained these results as follows:Each trait is determined by “factors” we now calll)......................... The genes which control the “opposing”traits of a characteristic are called m)................................, orn).................................. genes. For each characteristic, anorganism always has o)........... genes, which may bep)................................. (homozygous), or may be different(called q).........................................) In sexual reproduction,the r).................................. (eg sperm/eggs) contain only 1 ofthe genes for each trait. When the gametes unite ats).........................................., one gene from eacht).............................. are brought together in each offspring.

One of the alleles is dominant to the other, which is calledu)........................................ The v)...................................... genewill always show its effect, but the recessive one can only beexpressed in the case where it is w)......................-zygous.The appearance of an organism due to its genes is calledthe x)..........................................., while the “genotype” is they).................................................................................................

Mendel was successful, where others had failed, because:1. he chose z)...................................................... characteristics2. he began with aa)............................................ parent plants3. he bred ab)................... numbers of plants so the numbersof offspring would be ac)........................................ significant.

However, Mendel’s achievements were not recognisedbecause he was not ad)............................................................and because his findings were published in an obscurejournal written in ae)........................................... and did notcome to the attention of the scientific community untilafter his death.

Part B Mendelian Genetics Problems

1. In pea plants, green seed pods (G) is a dominant traitover yellow seed pods (g)a) What is the phenotype of a plant, if the genotype is:

i) GG? ii) gg? iii) Gg?

b) What is the genotype of a plant with seed pods that are:i) green, and it is pure-breeding?ii) heterozygous?iii) yellow?

(continued...)c) Use a punnett square to predict the outcome of each ofthe following crosses. In each case, state the expectedphenotypes of the offspring as a percentage.

i) Gg x Ggii) Gg x GGiii) gg x GGiv) Gg x gg

2. In rats, black fur (B) is dominant to brown (b).a) If a pure-breeding black rat mated with a pure-breedingbrown rat, what would be the

i) genotypes of the offspring?ii) phenotypes of the offspring?

b) One of the offspring from the cross described in part (a)was crossed with a brown rat.

i) Use a punnett square to predict the outcome.ii) In fact, they produced 7 babies; 5 black & 2 brown.

Is this result surprising? Explain your answer.

3. In humans, some people have little fingers that arestraight, while others have curved little fingers. Thischaracteristic is inherited by simple Mendelian inheritance.Study the following pedigree diagram, then answer thequestions which follow..Shaded shapes represent curved little fingers.

a) Is the curved little fingers trait dominant or recessive?Explain your answer referring to specific individuals above.

b) Assign the letters “S” and “s” appropriately to the 2alleles operating in this pedigree.

c) Extra information: individuals 2 & 4 are homozygous.Using the symbols chosen, work out the genotypes ofeveryone in the pedigree, as far as is possible.

d) Couple 1 & 2 had children who all have straight fingers.Was there any chance they might have had a child withcurved little fingers? Explain your answer.

e) Person 5 later married a girl with curved little fingers. Usea punnett square to predict the finger shapes of theirchildren.

f) In fact, person 5 and his wife had 2 beautiful little girlsboth with straight fingers. Is this possible? Is yourprediction wrong?

CHECK YOUR ANSWERS AT THE BACK

14



11

55

22 33 44

66 77 88 99

11111100

I

II

III



2 Daughtercells

IIddeennttiiccaall ttoo eeaacchh ootthheerr aanndd ttooppaarreenntt cceellll

4 Gametecells

NNOOTT iiddeennttiiccaall ttoo eeaacchh ootthheerr,,nnoorr ttoo ppaarreenntt cceellll



15

ChromosomesMendel’s discoveries were “re-discovered” by mainstreamscience in 1900. At about the same time, new techniques inusing stains to highlight specific parts of the cell had led tothe discovery of chromosomes. The combination ofMendelian Genetics + Chromosomes was the next bigbreakthrough. Things to know...

• Chromosomes are thread-like structures in thenucleus of cells. They only become visible (to a lightmicroscope) during cell division.

• Chromosomes have genes along their length.There may be 1000’s of genes on a chromosome.

• Chromosomes occur in pairs.Chromosomes in a pair are called “homologous”.Homologous chromosomes correspond with each other bycarrying allelic genes in corresponding locations.

Study this diagram to get theidea.

Consider 3 sets of genes.Genotype is AaBbCc.(heterozygous for eachcharacteristic)

This is how the genes could belocated on somechromosomes.

Notice that homologous pairscorrespond with each other, but are NOT identical.

• Before cell division, each chromosome is duplicated.

Study the diagram.

The original and its exact copyremain attached to each other,as a double chromosome.

Each strand of a doublechromosome is called a“Chromatid”.

The chromatids in a doublechromosome are identical...(look at the genes in thediagram) but the homologouspartners are not identical...merely corresponding.

Mitosis & MeiosisYou should already be familiar with the difference betweenthese processes of cell division in terms of their outcomes.

Now look more carefully at what happens to thechromosomes during each process.

3. CHROMOSOMES & DNA STRUCTURE

HHoommoollooggoouuss ppaaiirr

AAnnootthheerr HHoommoollooggoouuss ppaaiirr

HHoommoollooggoouuss ppaaiirr ooffDDoouubbllee cchhrroommoossoommeess

Indentical Chromatids ineach chromosome

ORIGINAL BODYCELL

with 4chromosomes(2 homologous

pairs)

This cell is “DDIIPPLLOOIIDD”(abbrev. “22nn”)

(chromosomes in pairs)

In this case,22nn == 44

DDIIPPLLOOIIDD22nn == 44

HHAAPPLLOOIIDDnn == 22

Mitosis Meiosis

In BOTHprocesses, thechromosomes

are firstduplicated, toform double

chromosomes

Homologouspairs have

separated, andcell divides in 2.

Now cells divideagain, and

separate thechromatids

Chromatidsseparate

Cell Dividesin 2

“HHaapp

llooiidd

” m

eans

hal

f the

chro

mos

ome

num

ber.

The

chro

mos

omes

are

not

in p

airs

.

AAaa

BBbb

CC cc

AA AA

BB BB

aa aa

bb bb

CC CC cc cc

Chromosomesline up in assiinnggllee lliinnee

Chromosomesline up in theirhhoommoollooggoouuss

ppaaiirrss



16

Chromosomes & Mendel’s GenesIn 1902, two scientists independently noticed a similaritybetween the way that chromosomes behaved in meiosis,compared to how Mendel’s genes were inherited.

Walter Sutton (USA) and Theodor Boveri (Germany) hadboth been studying meiosis using new staining techniqueswhich made chromosomes more visible. Both were awareof Mendel’s discoveries, which had been “re-discovered”just 2 years before.

The obvious similaries made it clear that the genes mustbe located on the chromosomes in the cell nucleus.

Chromosomes Contain DNAChemical analysis reveals that chromosomes are made ofDeoxyribonucleic Acid (DNA for short) wrapped inproteins.

We now know that DNA is a double helix-shaped moleculewhich carries a chemical code... it is a gene.

Each chromosome contains 1000’s of DNA molecules(wrapped in protein) each one specifying one of theorganism’s many hereditary traits.

The Structure of DNALike many biological molecules, DNA is a polymer, madeof many smaller units which are joined in long chains. Thebasic unit of DNA is a “Nucleotide”. (named for nucleus)

The 4 different bases are usually known just by the firstletter of each name:

A AdenineC CytosineG GuanineT Thymine

DNA molecules are composed of 2 strands of nucleotides(one running “upside-down” compared to the other) whichare joined by the bonding between “base” molecules.

Finally, the entiremolecule iscorkscrewed into a“double helix”, ratherlike a spiral staircase or ladder.



Chromosomes Mendel’s During Meiosis Genes

Begin in homologous Two genes for eachpairs characteristic

Pairs separate The 2 genes separatein meiosis in gamete formation

Gametes have only 1 Gametes have only 1of each chromosome of each gene pairpair (haploid)

At fertilization, each At fertilization, eachgamete supplies one gamete supplies onechromosome, so the gene, so the offspringzygote gets back to gets back to havinghaving paired chromo- two genes persomes (Diploid) characteristic

SimulatedPhotograph ofHumanChromosomes

PPaarrtt ooff aa DDNNAAmmoolleeccuullee

AA sseeccttiioonn ooff DDNNAA ccaarrrriieessaa ccooddee ttoo ssppeecciiffyy oonneeffeeaattuurree ooff tthhee oorrggaanniissmm;;

== aa ggeennee

A NUCLEOTIDE

PPhhoosspphhaatteeggrroouupp

SSuuggaarr((DDeeooxxyyrriibboossee))

“Base” moleculeThere are 4different bases, so4 nucleotides are inDNA

One Nucleotide

Two Strands of Nucleotide Chains

BBaasseess AA-TT bboonnddeedd

BBaasseess CC-GG bboonnddeedd

Bases are the“steps” of aladder

Sugars & phosphatesare the side rails

A

A

G

G

T

T

C

C

Notice that the onlybase combinations are

A-TT and C-GG



17

Non-Mendelian InheritanceGregor Mendel discovered the basics of Genetics, but itwas found early in the 20th century that genes don’t alwayswork in that simple “Mendelian” fashion.

Thomas Morgan began experimenting with Drosophila fruitflies and quickly found they were ideal for geneticsexperiments. They bred quickly in large numbers, were easyto feed and keep in small bottles, and showed manydifferent genetic traits that could be studied.

In 1910, in an experiment involving flies with different eyecolours, Morgan realized that the way this characteristicwas being inherited depended on the sex of the fly... malesand females were inheriting eye colour differently.

What Determines Sex?In humans, and in many other species, sex is determined bya special pair of chromosomes... the “sex chromosomes”.

In a normal human body cell there are 46 chromosomesarranged in 23 homologous pairs. Of these, 22 pairs arecalled “autosomes” and are the same size and shape inmales as in females.

The 23rd pair are the “sex chromosomes”:

Females have a matching pair ofchromosomesthat are known as “X” chromosomes.A female is described as “XX”

Males have one “X” chromosome,and one smaller “y” chromosome.Males are described as being “Xy”

How these chromosomes are passed on to children can beshown using the Punnett Square diagram to track, notgenes, but the sex chromosomes:

Notice thatfemales can onlypass on an Xchromosome intheir eggs.

Male’s spermcells can eithercarry an X or a y

Which type ofsperm fertilizesthe eggdetermines thesex of the baby.

Sex-Linkage InheritanceWhat Thomas Morgan noticed in 1910 was that the eyecolours he was studying in Drosophila fruit flies were notbeing inherited equally by males and females... the traitswere linked to the sex of the flies... “sex-linkage”.

The common and normal eye colour in the flies is red.Morgan discovered a male fly with white eyes.He set out to do a “Mendel-type” breeding experiment:

PARENTS

F1 generation

All have red eyes.Morgan concluded (correctly)Red is DOMINANT,White RECESSIVE

F2generation

Females 100% red-eyed. Males 50%: 50%What’s going on?

Morgan produced hundreds of flies in the experiment so,like Mendel, his results were statistically significant.

The Explanation:The genes for eye colour is carried on the X chromosome.The dominant (Red) gene can be designated as “XR ”The recessive (White) gene is “Xr ”The male “y” chromosome does NOT carry one of thesealleles at all.

The possible female (XX) genotypes & phenotypes are:

XRXR Red eye female (homozygous)XRXr Red eye female (heterozygous)XrXr White eye female

The possible male (Xy) genotypes & phenotypes are:

XRy Red eye maleXry White eye male

Note that females get 2 genes, but males only get onebecause their “y” chromosome lacks this allele totally. Amale cannot be heterozygous for this trait and cannot havea “hidden” recessive gene.

WHEN DOING PUNNETT SQUARES WITH SEX-LINKAGE, YOU MUST TRACK THE “X” AND “y”CHROMOSOMES... see next page.



Xy XX

X & y X & X

X X

X

y Xy

XX

Xy

XX

x

gametes

PPhheennoottyyppeess ooff OOffffsspprriinnggGGiirrllss :: BBooyyss

11 :: 115500%% :: 5500%%

Girls

Boys

Father Mother

X

White-eyed Red-eyedMale Female

F1 flies wereallowed to mateamongthemselves



18

Morgans’s Sex-Linkage Experiment (continued...)Here is the experiment explained by Punnett Square.

Then, the F1 generation were allowed to breed amongthemselves. Notice that the F1 females are all heterozygousred eyed ( XRXr ) and the males are all red eyed ( XRy ).

There are a number of genes in humans that are sex-linked.The best-known are 2 genetic disorders:

• Red-Green Colour Blindness, is where a person cannotdistinguish between certain colours.

• Haemophilia, is a condition in which the blood does notclot properly, putting the person at constant risk ofinternal bleeding. It was always a fatal condition, but inmodern times people with haemophilia are treated with“clotting factors” from donated blood.

Both conditions are sex-linked, inherited as recessive geneson the “X” chromosome. They occur much more often inmales than females.

Inheritance by Co-DominanceAnother example of “Non-Mendelian Inheritance” isknown as “Co-Dominance”. This is a fairly commonsituation in which the 2 alleles for a characteristic do notshow a Dominant-Recessive pattern, but when both genesare present (heterzygous) they are both expressed, and mayresult in an “in-between” phenotype.

Example: In Shorthorn cattle, there is gene (R) that causesthe hair of the animal’s coat to be “red” (actually a rusty-brown colour). To be red, the animal must be homozygousfor this gene.

Genotype RR

The other allelic gene (W) causes the coat to be white, if theanimal is homozygous.

Genotype WW

If an animal is heterozygous, with both alleles present,neither gene dominates the other. Both genes areexpressed, producing mottled patterns of red and whitehair which is called “roan”.

Genotype RW

Note that it is best to use 2 different CAPITAL letters assymbols in this case, since neither gene is recessive.

Here is what happens in a “Mendel-type” cross:

PARENTS

gametes: R only W only

F1100% Roan

gametes: R or W

F2

Phenotypes: RED : ROAN : WHITE1 : 2 : 1

25% : 50% : 25%Try to verify for yourself the F2 result by using aPunnett Square.



Xrry XRRXRR

Xrr & y XRR & XRR

XRR XRR

Xrr

y XRRy

XRRXrr

XRRy

XRRXrr

x

gametes

PPhheennoottyyppeess ooff OOffffsspprriinngg ((bbootthh sseexxeess))RReedd::WWhhiittee

11 :: 00110000%% :: 00

Parents

The F11 are allred-eeyed.Note thatfemales are allheterozygous.

XRRy XRRXrr

XRR & y XRR & Xrr

XRR Xrr

XRR

y XRRy

XRRXRR

Xrry

XRRXrr

x

gametes

PPhheennoottyyppeess ooff OOffffsspprriinnggFFEEMMAALLEESS MMAALLEESSRReedd :: WWhhiittee RReedd :: WWhhiittee

110000%% :: 00 5500%% :: 5500%%

The F22 arered : white

3 : 1just likeMendel’sresults, butthe sexes aredifferent.

TRY THE PROBLEMS IN WORKSHEET 3 TRY THE PROBLEMS IN WORKSHEET 3

XRR

RR

WW

WW

RW RW RW

RW RW

RW

FF1 bbrreeeedd aammoonnggtthheemmsseellvveess




19

The Effect of EnvironmentIt’s not just an organism’s genes that produce itsphenotype; the environment has an effect as well.

For example, consider some of Mendel’s pea plants withdifferent genes for stem height.

Now, imagine planting them (as baby seedlings) in verypoor soil, so that normal growth was not possible.

The point is that the genes may control what the organismCOULD grow up to be, but the environment may influencethis, possibly altering the final appearance (phenotype).

In Hydrangea plants, if cuttings are taken from a singleindividual (the cuttings would be genetically identical) andgrown in different soils, the flowers on each cutting canbe different colours. If the soil is slightly acidic theflowers will be blue, but in slightly basic soil they’ll bepink.

Identical twins have inherited exactly the same genes. In theUSA about 40 years ago, a famous study was done onidentical twins who had been adopted into separate familiesand raised in different environments. The study found quitelarge differences between the twins in intelligence,personality, and even appearance. Presumably thesedifferences were due to different foods, education, etc.

Genotype TT

Phenotype DWARF

Genotype tt

Phenotype DWARF

Genotype TT

Phenotype TALL

Genotype tt

Phenotype DWARF

IN GOOD SOIL

IN POOR SOIL

Variation Caused by Sexual ReproductionThe simple fact that sexual reproduction involves TWOparents, creates a lot of variation. The offspring receivesgenes from 2 different individuals, thereby getting a new“mix” of traits.

Variation Caused by MeiosisThe process of meiosis to produce the sperm and egg cellsincreases variation, even before fertilization occurs.

Study the diagram of meiosis on page 15.Remember that homologous chromosomes are NOTidentical.

Each pair of homologous chromosomes line up andseparate at random, and independently of all other pairs, sothe number of different possible gametes is very large. Inhumans, with 23 pairs of chromosomes, it is possible formeiosis to produce about 8 million different combinationsof chromosomes in the gametes of each person!

But wait! ...there’s more:Crossing-OverDuring meiosis homologous chromosomes also swappieces of chromatid with each other, further mixing up thepossible gene combinations:

GAMETE FORMATION WITHOUT CROSSING-OOVER

WITH CROSSING-OOVER

Possible genecombinationsin gametes

or

Possible genecombinationsin gametes

MEIOSIS

MEIOSIS

AB

aBAB

ab

abAb

Genetics, Sex and EvolutionDuring his lifetime, Charles Darwin freely admitted thatthere were 2 big gaps in his controversial Theory ofEvolution...• How were characteristics inherited?

When the “fittest” survive and breed, how do they passon their “survival traits” to their offspring?

• Where does variation come from?Natural Selection needs differences between individualsto choose the survivors. Why is there variation anyway?

The Science of Genetics can now explain that

Part of the answer to that is in the process ofMEIOSIS

and sexual reproduction

These chromosomes have exchangedpieces of chromatid with each other.

This has mixed up the combinations ofgenes “A”, “a”, “B” and “b”.

In Summary...

Variation is important for Survival of the Species,and for Natural Selection

to choose the survivors for Evolution.

Variation in sexually-reproducing species comes from:• combining gametes from 2 different parents• Independent Segregation of all the pairs of

homologous chromosomes during Meiosis• Crossing-Over process during Meiosis

In the next section, you will find out how NEWvariations appear in the first place.

AA AA

BB BB

aa aa

bb

AA

BB BB

aa

bb bb

bb

Remember, each gamete gets just one of these 4 chromatids

AAaa


Chromosomes are thread-like structures in the a)............................of a cell. They are only visible during b)...............................................Chromosomes come in pairs, referred to as c)....................................The members of a c)..................................... pair are not identical,but correspond with each other because they carryd)............................................... genes in corresponding locations.Before a cell division, each chromosome is e).....................................to make a “double chromosome”. The 2 parts are calledf)............................................. and they are g)........................................to each other.

In Mitosis, the chromosomes line up h)...............................................and the i)............................................... separate, so that the daughtercells are j)............................................... to each other, and to thek).................................... cell.

In Meiosis, the chromosomes line up l)......................................... andthe first division separates the m)............................................... pairs.Then the cells divide again to form n)................ (number) gametes,each with o)....................... the original number of chromosomes.Body cells with pairs of chromosomes are called p)...........................while gametes are said to be q)........................................... Humanbody cells have a total of r).................... (number) chromosomes,while egg or sperm cells have s)............... (number)

Part B Problems in Sex-Linkage & Co-DominanceCheck your answers at the back.1. Refer to Morgan’s experiment with fruit flies, pages 17-18.a) Why are there 3 genotypes for female flies, but only 2 for males?b) From which parent (mother or father) does a white-eye male flyinherit his white eyes? Explain.c) i) What is the genotype of a female, who is heterozygous?

ii) What is her phenotype?iii) Explain why this genotype is often referred to as a

“carrier” female.d) Use a Punnett Square to predict the outcome of each cross:(You must track the X & y chromosomes.Offspring phenotypes should describe the sexes separately)

i) Xry crossed with XRXr

ii) XRy crossed with XrXr

2. In humans, a recessive gene (“Xn”) carried on the Xchromosome causes colour-blindness. The “normal vision” genecan be symbolized by “XN”. Use these symbols to write thegenotype of:a) a homozygous normal-vision female.b) a normal-vision male.c) a colour-blind male.d) a colour-blind female.e) a “carrier female” (heterozygous)f) A man with normal vision married a woman who is colourblind. Use a Punnett Square to predict the pattern of inheritancein their children.

20



In 1902, two scientists t).....................................and..............................noticed the similarities between how Mendel’s genes worked andhow u)..................................... behave during v)....................................From this observation it was clear that w).............................................................................................................................................................

Chromosomes have been analysed chemically and found tocontain x)................................................. and ............................ It isknown that the DNA molecules contain a chemical code which isa y)........................ Thus, each chromosome contains many genes,each one encoded by a molecule of z)....................

The DNA molecule is a aa).......................... of repeating unitscalled ab).................................... Each one is made of 3 smallerparts; ac)........................... and ............................... and .........................There are 4 different “bases”, known by the intial letters of theirnames; ad)......, .........., .......... and .......... (letters) The DNAmolecule is a double- ae)..................... shape, made of af)...............(number) strands resembling a twisted ladder. The “rungs” of theladder are formed by 2 “bases” bonding with each other. Thebases can only bond in combinations ag)...................... and...............

Sexual reproduction produces variations in a population because:• Offspring receive ah)...........................................................................• ai).................................................... of homol.chromos. in meiosis• the process of aj)....................................................... in meiosis.

3. Refer to the information about Co-Dominance, page 18.Use Punnett Squares to predict the phenotypes of calves born if:a) a roan bull mated with a red cow.b) a white bull mated with a roan cow.

4. In a particular breed of chickens, the feather colour iscontrolled by 2 alleles “B” and “W”. Genotype BB produces blackfeathers. Genotype WW produces white feathers. Theheterozygous genotype BW results in black & white “speckled”feathers.Use a Punnett Square to predict the colours of chicks from:a) a speckled rooster and speckled hen.b) a black hen and a white rooster.c) a black rooster and a speckled hen.

5. Some plants have flower colours controlled as follows:There are only 2 alleles involved, but there are 3 phenotypespossible... red flowers, white flowers and pink flowers.a) Suggest how just 2 genes can result in 3 different colours.b) Suggest suitable symbols for the alleles.c) Use these symbols to write the genotype for:

i) red flowerii) pink floweriii) white flower

d) Use a Punnett Square to predict the phenotypes resulting fromcrossing a red-flowering plant with a white-flowering plant andbreeding through to the F2 in a “Mendel-type” experiment.

Worksheet 3 Part A Fill in the blanks





21

How DNA Structure Was DiscoveredBy the middle of the 20th century it was suspected thatDNA was probably the “genetic chemical” and it wasknown that it contained sugar, phosphate and the 4 basesA,C,G and T. What no-one could understand was, if DNAwas the genes, how could it:

• Replicate (duplicate) itself for cell division?• Control the phenotype of an organism?

It seemed likely that the key to this problem was to find outthe structure of the DNA molecule. The story of whathappened is a classic example of how Science and scientistsmake progress using collaboration and communication.

In 1953, English scientist Francis Crick had become anexpert at interpreting the shapes of molecules using thenew technique of “X-ray Diffraction”.

Meanwhile, at another laboratory, Maurice Wilkins (NewZealand) managed to prepare a pure crystal of DNA, andRosalind Franklin (England) was able to get an X-RayDiffraction image of it, but neither understood how tomake any sense of the pattern it produced.

Then a young American, James Watson, who was interestedin understanding the DNA mystery, visited the Wilkins-Franklin laboratory. With their collaboration, he took theirdata to Crick for his expert interpretation. Between them,Watson and Crick made one of the most notable scientific

breakthroughs in the history of Biology... they figured outthe base-pairing, double-helix structure of DNA andrealized immediately how this structure could lend itself toreplication... an essential feature of a gene.

No one of these scientists could have made progress alone.Each had certain data, or skills or expertise, but only bybringing it all together was the great discovery possible.Success came from different people communicating andunselfishly sharing their knowledge and talents.

DNA ReplicationSo how does the structure of the DNA molecule lend itselfto replication?

The key is the way the complementary bases bond togetherin the double stranded structure.

This means that if you have ONE STRAND of a DNAmolecule it is a “mirror-image” template for the other. Ifyou split a DNA molecule into 2 separate strands, eachstrand can be used to build a new, complementary strand.

That’s exactly what happens to all the DNA in eachchromosome, before a cell division occurs.

4. MOLECULAR GENETICS & MUTATION

Base-ppairing

Double-sstrandedHelix

sugar-phosphate “side rail”A G T C C A

BasesT C A G G T

The only combinations that will bond areA-TT and C-GG

G CT AC GC GA T

CTAAGCGATCG

GATTCGCTAGC

TCGCTAGC

AGCGATCG

A

A

A

A

T

T

G

G

C

CC

C

GG

G

T

T

T

CA

GT

DNAREPLICATION Original, double-

stranded DNA

Molecule is untwistedand “unzipped” byenzymes “Spare” nucleotides

Nucleotidesmatch up withcomplementarybase on originalstrand.

Enzymesconnect them inplace, forminga new strand

Whencompleted,each new DNAmolecule istwisted backinto a double-helix shape

“old” strand

“New” strand TWO IDENTICAL DNAMOLECULES

This is how the DNA molecules,which are the genes on the chromosomes,

are replicated in preparation for cell division.



22

How Can DNA Control a Phenotype?To answer this question, you need to be reminded aboutthe structure, and the role, of proteins.

Protein Structurehas been covered briefly in previous topics. Here’s a quickrevision:

The exact shape of the final protein depends on thesequence of the amino acids in the polypeptide chain.There are about 20 different amino acids, and some ofthem are attracted to (or repelled from) each other, so howthe chain twists and folds upon itself depends on exactlywhich ones are located where.

Protein FunctionsProteins have many functions within an organism:

• Enzymes are all protein molecules

• Structural Molecules, such as in muscle fibres, skin, hair and bone matrix are proteins.

• Many “Special Molecules” are proteins, such as haemoglobin (the oxygen carrier in blood)chlorophyll (absorbs light for photosynthesis)antibodies (which help fight disease)... and many more.

In every case, it is the shape of the protein molecule whichis essential to its correct functioning... Enzymes can onlyconnect to their substrate if their shape is right....Haemoglobin can only pick up oxygen if the shape iscorrect... and so on.

DNA and Protein SynthesisThe sequence of bases in the DNA molecule is a code.Each 3 bases are a “code word” (a “Codon”) whichspecifies an amino acid to go into the polypeptide chain.

If a polypeptide containing 1,000 amino acids is needed,then a DNA molecule made up of 3,000 nucleotide bases,will be the gene for this polypeptide.

Only one strand of the double-helix of DNA is the gene.The other “mirror-image” strand is present only to allowthe gene to be replicated for cell divisions.

How the DNA base sequence gets to make a functioningprotein which then produces a phenotype is explained by asimple model on the next page.

The Changing Definitions of a “Gene”When studying Genetics at the organism level:

a “gene” = the hereditary unit which determines one traitin the organism’s phenotype.

However, at the molecular level a new definition is needed.

In the 1940’s, two American scientists, George Beadle andEdward Tatum discovered the connection of genes toproteins. Studying a genetic defect in a common fungus,they found that there were 3 different genes that couldproduce the same defective phenotype.

Beadle and Tatum realized that each enzyme 1,2 & 3 musthave a separate gene. The phenotype “S-defect” could beproduced by a defect to the gene for enzyme 1, or the genefor enzyme 2, or the gene for enzyme 3. So, the newdefinition for a gene became:

a “gene” = a unit of heredity that specifies one protein

But now that we know about DNA, and that some proteinsrequire more than one polypeptide chain...



PROTEINS are polymers of Amino Acids.

Amino Acidmolecules a “Polypeptide” chain may contain

1000’s of amino acids

AA PPoollyyppeeppttiiddee iiss NNOOTT aa pprrootteeiinn uunnttiill iitt ffoollddss aannddttwwiissttss iinnttoo aa ffiinnaall,, 33-DD sshhaappee..SSoommeettiimmeess,, sseevveerraall ppoollyyppeeppttiiddeess jjooiinn ttooggeetthheerrttoo ffoorrmm tthhee ffiinnaall pprrootteeiinn mmoolleeccuullee

Proteinwith precise3-D shape

Proteins carry out many vital functions

Correct functioning depends on the exactsequence of amino acids in the polypeptide chain

IT IS THE DNA WHICH CONTROLS THEAMINO ACID SEQUENCE

DNA StrandBases T A C T G G C A T C A A

Codon

Amino Acids forming a Polypeptide

Normal Chemical Pathway in Fungi Cells

P,Q,R and S are cell chemicals. If any reaction isblocked, then “S” cannot be made, and the

organism has a chemical defect

Enzyme 1 Enzyme 2 Enzyme 3P Q R S

A “Gene” isa DNA molecule

which specifies one polypeptide

EENNZZYYMMEE




23

then,Part 2. From Polypeptide to Phenotype

How DNA Causes a Phenotype: Part 1. From DNA to Polypeptide

The initial step is calledTRANSCRIPTION

DDNNAA mm-RRNNAA

One strand of the DNA (the gene)acts as a “template” for the

production of a single-stranded“messenger RNA” (m-RNA)

RNA is a polymer ofnucleotides, similar toDNA, but

• single strand only• different sugar• one different

nucleotide mm-RRNNAA

You should recallthat the Ribosomes are

organelles responsible forprotein synthesis in cells

Amino Acids are carriedinto position by t-RNA

(“Transfer RNA”)molecules

tt-RRNNAA’’ssAAmmiinnooAAcciiddss

The polypeptide chaintwists and folds to

form a proteinPossibly it is combinedwith other polypeptides

or special chemicalgroups to form...

Perhaps it’s astructural protein,

used to buildmuscle or skin

Maybe it becomes amolecule of

Haemoglobin, usedto carry oxygen in

the blood

It could be a Hormone,which controls some

aspect of HomeostasisIt could be anENZYME, able to

catalyse a chemicalreaction

EEnnzzyymmee

SSuubbssttrraatteess

STARTINGCHEMICALS(Substrates) Enzyme catalyses reaction(s)

to produce coloured pigmentin cells of the iris of the eye

The next step is calledTRANSLATION

Product;a Coloured

Pigment

EEaacchh 33-bbaassee ““ccooddoonn””

iinn mm-RRNNAAssppeecciiffiieess

oonnee aammiinnoo aacciiddiinn tthhee

ppoollyyppeeppttiiddee cchhaaiinn

TThhiiss ooccccuurrss iinn tthheennuucclleeuuss

RRiibboossoommeemoves along

m-RNA

Ribosome enzymesconnect the amino

acids to form apolypeptide chain

m-RNA moves

from the nucleus out to a ribosome

Polypeptide chain

growing by addition of Ammino Acids

a functionalPROTEIN molecule

Example: Eye Colour

The colour of your eyes is agenetically determined phenotype.The coloured pigment is made by

enzymes, which are proteins,coded in your DNA

The gene(s) for eye colour are present in every cell of your body, but are only expressed in your iris cells.Similarly, the genes for liver functions are only expressed in your liver cells, and genes to make taste buds are

only expressed in your tongue. What controls which genes are expressed is still unknown in most cases.



24

MutationIn all organisms, cells divide all the time. There’s mitosis tomake new cells for growth, and meiosis to make gametesfor sexual reproduction. Whenever a cell is about to divide,the chromosomes are replicated and all the DNA theycontain makes an exact copy of itself.

But sometimes mistakes happen...

• Errors can occur in duplicating the DNA• Chromosomes get broken, then incorrectly repaired and

sometimes an entire chromosome just gets “lost”.

Any accidental change to the genetic material is a Mutation.

Causes of MutationSome mutations do not have any discernible cause... theyare just accidents that happen. However, it is known thatcertain factors can increase the likelihood of mutations.These factors are called mutagens, and include:

• Higher Temperatures. Mutation rates are higher in hotterclimates than colder climates.

• Certain Chemicals, for example pesticide chemicals suchas the infamous “agent orange”.

• Radiation, including X-rays, nuclear radiation and ultra-violet radiation from the Sun.

Evidence for Mutagenic Nature of Radiation• Controlled experiments have demonstrated that geneticchanges can be induced in living things (eg plant seeds,fungi, fruit flies etc) by exposing them to doses of X-rays,or nuclear radiations.

• Medical records from Japan following the Atom Bombattack on Hiroshima (1945) indicate a huge increase ingenetic mutations among the people in the years following.

• Countries like Australia, with a sunny climate and outdoorlifestyle, have high rates of skin cancer. These cancers arebelieved to be due (at least in part) to the mutagenicproperties of UV light.

Changing the DNA Can Produce a new GeneYou will see at the bottom of this page that mutations canhave many possible effects, ranging from absolutelynothing, to a new inheritable characteristic. How could anew characteristic happen?

Imagine an accidental change to just 1 base in a DNA strand.

Just one amino acid being different may alter the way thepolypeptide folds into its 3-D shape. This could alter theshape of an enzyme molecule, so that instead of producing(say) Blue-Eye Phenotype, it produces a new colour pigment.



Mutation during MitosisAffects a Body Cell

Mutationmight

have noeffect on

cell.

Mutation mightcause malfunction

in cell, whichbecomes cancerous.

Organism seriouslyaffected, but futuregenerations are not.

Gamete NOTinvolved in

reproduction.No effect.

Offspring might get new inheritable gene.New trait might be:

• detrimental; less chance to survive.• an improvement; helps survival.• neither good nor bad, just different.

The mutation becomes a new variation to beinherited by future generations

Cell mightnot be ableto functionproperly.Cell dies.

No effect onmulticellularorganism.

Effects of MutationIt depends on what sort ofcell the mutation occurs in.

Original DNA StrandBases T A C T G G C A T C A A

Codon

Amino Acids forming a Polypeptide

Change will occurhere

Altered DNA StrandBases T A C T G G A A T C A A

Codon

1 Amino Acid will be different in thepolypeptide

Changed base

SubstrateChemical

NNeewwCCoolloouurr

PPiiggmmeenntt

BBlluueePPiiggmmeennttiinn iirriiss

originalEnzyme

MutatedEnzyme

OriginalPhenotype(Blue eyes)

MutantPhenotype(new colour)

Mutation during MeiosisAffects a Gamete

Gamete involved in fertilization



25

Mutation and EvolutionMutations occur at random in the DNA molecules andchromosomes. Most are detrimental to the cell in whichthey occur, but occasionally a mutation produces a new,inheritable trait in an offspring.

Usually, new mutant genes are recessive alleles. Beingrecessive, they can be inherited through many generationswithout ever being visible in the population. Only when 2heterozygous individuals mate and bring together a pair ofrecessive genes does the new phenotype actually appear.

The new phenotype might be quite a trivial difference...• slightly bigger ears• slightly shorter toes• a new colour pigment in the fur• a slightly longer intestine ... and so on.

However, it is such small differences that give the variationto a population for Natural Selection to work on.

Finally, Darwin & Wallace’s Theory of Evolution iscomplete...

1. All organisms produce more offspring than can survive.

2. In every species there is variation.New traits originate from genetic mutation.Traits are mixed in new combinations by meiosis andsexual reproduction, producing greater variation.

3. Natural Selection chooses the survivors.

4. The “Fittest” individuals pass on their characteristics asgenes (DNA) inherited by the processes of Genetics.

5. Over generations, a species evolves.

Punctuated EquilibriumDarwin always imagined that evolution was a very slowprocess, taking at least 100,000 generations over perhapsmillions of years, for a species to change significantly. Thefact that the fossils showed significant change from onerock layer to the next was simply, in Darwin’s opinion, dueto the “patchiness” of the fossil record, giving us just aglimpse here and there of the slow and steady changesgoing on.

An alternative explanation was proposed in the 1970’s. Thisidea, called “Punctuated Equilibrium” suggests thatevolution does not occur in a slow and steady way, but inshort, sharp bursts of rapid change, in between longperiods of little or no change at all. It is suggested that aspecies might change significantly within just a fewthousand years rather than millions.

Evidence for Punctuated Equilibrium• Some fossil sequences show the same species existing,apparently unchanged, for millions of years, then suddenly“disappearing” and being replaced by a different (butobviously similar) species. Perhaps it rapidly evolved intothe “new” species?

• Studies on living populations (eg snails in grasslands)show that if the environment changes suddenly (eg becauseof humans clearing the land) the species can respond witha very rapid genetic shift within 20 years or so. This doesnot prove that a new species can evolve quickly, but lendssupport to the idea of rapid change.

The debate continues...



Sexual Reproduction and Meiosis keep mixing the genes in new

combinations,

but the original source of variation is MUTATION

SSLLOO

WW,, SS

TTEEAADD

YY CCHH

AANNGG

EESS OO

VVEERR

TTIIMM

EE

......TTHHEENN AA RRAAPPIIDD BBUURRSSTT OOFF CCHHAANNGGEESS

NNOOCCHH

AANNGGEE

......

SSTTAABB

LLEEAAGG

AAIINN

EVOLUTION byGRADUALISM

EVOLUTION byPUNCTUATEDEQUILIBRIUM

AAuussttrraalliiaann aanniimmaallss hhaavvee eevvoollvveeddttoo ssuurrvviivvee aanndd tthhrriivvee

iinn aa hhaarrsshh aanndd uunnpprreeddiiccttaabblleeeennvviirroonnmmeenntt

PPhhoottoo bbyy DDiiaannaa

Worksheet 4Fill in the blanks. Check your answers at theback.

The discovery of the structure of DNA shows how gooda)............................................ and b).............................................contribute to scientific progress. Mauricec).................................... was able to prepare a crystal of pureDNA, and Rosalind d)............................................. was able toget an X-ray Diffraction image of the crystal, but neither ofthem could interpret it. James e)................................collaborated with them, and took their data to Francisf)...................................... who had become an expert in thisnew technology.. Between them, Watson & Crick figuredout the double-helix shape and the g)..................-pairingstructure of DNA.

The h).......................-stranded structure, and thecomplementary base-pairing allows DNA molecules to bei)........................................ in preparation for a cellj)..................................... First, the DNA strandsk)................................................ Then each strand can act as al)................................................ for the making of a newcomplementary strand.. Each base specifies what must goon the new strand, because only bases m).......... & ................and bases n).............. & ..................... can go together. Oncea new strand is built onto each “old” strand, the result is 2o).................................... DNA molecules.

Proteins are polymers of p)......................................................A chain of p).................................................. is called a“q).......................................................... chain”. To become afunctioning protein, it must twist and fold into a preciser)............................................ Exactly how the chain twistsand folds depends on the exact s).............................. of theamino acids. There are about t)................. (number) differentamino acids and they may attract or u)...................................each other, causing the chain to twist and fold upon itself..

Some different types of proteins includev)............................... which catalyse metabolic reactions, andw)................................ proteins in muscles, skin and hair cells.In each case, it is the x)........................... of the protein whichis vital to its correct functioning. This shape is due to thesequence of y)....................... acids, and these are specified bythe base sequence of the z).....................................

In DNA each aa).............. (number) bases form a code word(called a ab)...................................) to specify one amino acid.The first step in the process is calledac)........................................... and involves the production ofa molecule of ad)............................ To do this, the “genestrand” of the DNA is used as a ae)..........................................to build the RNA from nucleotides. Compared to DNA,the RNA is only af).............................-stranded, and has adifferent ag)........................................... in the “backbone” ofthe molecule, and one differentah)..............................................

Next, the m-RNA moves out of the ai)...................................to one of the aj)............................................... Theseorganelles are the sites of proteinak)......................................... Here the second stage, calledal)......................................................., occurs. According to thecode of bases on the m-RNA, amino acids are placed one-by-one in sequence to build theam)........................................................... chain. Another formof RNA, called an)................................ carries each aminoacid into place. The enzymes of the ao)..................................then catalyse the reaction to join the amino acids to eachother.

To cause a phenotype to occur, the polypeptide chain mustthen twist and fold to form a functioningap).......................................... As an example, it could becomean enzyme, which aq)............................................ a chemicalreaction in the iris of the eye. The reaction might result inthe production of a coloured ar)..............................................which produces the phenotype of eye colour.

Any accidental as)................................... to a gene orchromosome is a at)............................................. Some do nothave any discernible cause, but there are certain factors,called au)...................................... which increase thelikelihood of a mutation. Higher av)......................................is one, and certain aw).................................... are known tobe mutagens. Various forms of radiation are mutagenic,including ax).................................. and ay).......................... andaz) ................................................

Altering just one base on a ba)....................... molecule cancreate a new gene. One different base could cause onebb).............................-acid to be different in thebc)............................................................ chain. This in turncould alter the bd)......................................... of a protein. Ifthis protein is an be)........................................., then the way itcatalyses a reaction could change, resulting in a differentchemical product. For example, this could result in adifferent bf)....................................... in the iris cells of theeye, and so a new phenotype for eye colour.

Mutations are significant for the Theory ofbg)................................ because they explain wherebh)............................... in a population comes from originally.

It has usually been accepted that evolution occurs with aslow and steady accumulation of changes. In the 1970’s anew idea, called bi)........................................................................................ was put forward. Thissuggests that species bj)............................................... for longperiods of time, and then undergo bk)....................................................................... of evolution.

26








27

Reproductive TechnologiesHumans have developed a number of techniques forcontrolling or enhancing the reproduction of crop plants,domesticated animals, and even themselves.

Artificial PollinationThis is the oldest and simplest reproductive technique.Gregor Mendel used this to control the reproduction of hispea plants, and it had probably been used for centuriesbefore that.

Very simply, it involves taking pollen from one (selected)plant and dusting it onto the flower of the other (selected)parent. This gives complete control over which plantsbecome the parents of the next generation.

In modern agriculture, almost all of our cereals, fruits andvegetables are now the result of artificial pollination. New“types” are created by artificial pollination using differentvarieties or even different species. Such “cross-breeds” arecalled “Hybrids”. For example, the “nectarine” is a hybridformed by crossing a peach with a plum.

Once commercially important varieties are created, hugenumbers of seeds are produced, again by artificialpollination of selected parent plants. This results inmillions of almost identical plants being grown in crop“monocultures”.

Commercially it has many advantages, such as greatconsistency in growth rates and food quality. Later, we willdiscuss possible disadvantages.

Artificial Insemination (A.I.)This is basically the animal equivalent. Semen can becollected from a champion bull, divided up into many smallsamples and frozen. Distributed anywhere in the world, itcan be thawed out and inserted into a fertile cow with ahigh chance of successful fertilization.

Thus a top-quality bull can become the father of manythousands of calves, thereby improving the quality of cattleherds all over the world.

This works too, for racehorses, dogs, sheep and so on.There are huge advantages, such as entire herds of high-quality beef cattle, but there may be disadvantages too...these will be discussed later.

Humans use A.I. for their own reproduction too. If a manis sterile, but he and his wife wish to have children, she canbe inseminated with semen from an anonymous donor.There are “sperm banks” of frozen semen for this use.No-one has seriously suggested using this to “improve” thehuman race... this would be an ethical & moral issue.

CloningA “clone” is a group of organisms which are all geneticallyidentical. The simplest form of cloning is asexualreproduction, which has been done artificially with plantsfor thousands of years.

Every time a plant is grown from a cutting, or by grafting,a clone is being created. Farmers and gardeners have beendoing this for thousands of years.

More recently, the process of “Tissue Culture” has allowedplant cloning on a massive scale. This involves takingthousands of small pieces of tissue (each perhaps just a fewcells) from a “parent” plant and culturing them in a nutrientliquid in a test tube in the laboratory. Eventually they growlarge enough to be planted out into soil to grow to be“adult” plants. This allows a clone of many thousands to begrown from just one parent plant.

Cloning of animals is much more difficult and the firstmammal clone was not achieved until the 1990’s with thefamous “Dolly” the sheep.

5. REPRODUCTIVE TECHNOLOGIES & GENETIC DIVERSITY

HOW TO CLONE A MAMMAL

PPAARREENNTT ooff CCLLOONNEE EEGGGG DDOONNOORR

BBooddyy CCeellll

DDiippllooiidd NNuucclleeuussEExxttrraacctteedd

NNuucclleeuussrreemmoovveedd

DDiippllooiidd NNuucclleeuuss ffrroommbbooddyy cceellll ppllaacceedd iinnttoo EEgggg

CCeellll

““FFeerrttiilliizzeedd”” eeggggppllaacceedd iinn uutteerruuss

NNoorrmmaall pprreeggnnaannccyyaanndd bbiirrtthh

SSuurrrrooggaatteeMMootthheerr

The baby lamb is genetically identical tothe single parent at top left.

It is an “identical twin”, except younger

UUnnffeerrttiilliizzeeddEEgggg



28

Reproductive Technologies & Genetic Diversity

Artificial Pollination, A.I. and cloning all have the potentialto diminish the Genetic Diversity of the species involved.All these processes, if used on a large scale, result in manyoffspring being produced from just a few, or even just one,parent. This means that all these offspring are closelyrelated to each other and have less genetic diversity.

Already, many of our food crops, such as wheat and rice,are “monocultures” of millions of individual plants whoare “siblings” from relatively few parents. In a bananaplantation, the entire population may be a clone ofgenetically identical plants grown from cuttings and“suckers” (asexual runners) from a single parent.

Among farm animals such as beef cattle, the widespreaduse of A.I. to improve herds has also lessened the geneticdiversity of those herds.

There are many benefits to this, but there may be seriousconsequences too. Remember that genetic diversity(“variation”) is essential for the long-term survival andevolution of a species. If a species has little variation, thenany change in the environment (eg a new disease, climatechange) might adversely affect ALL the population, andleave no survivors.

Transgenic SpeciesAs well as reproductive technologies, humans are alteringthe “gene pools” of species in another way...Genetic Engineering technology is able to transfer one ormore genes from one species to another to form“Transgenic Species”. Some examples:

Gene Transfer Purpose / BenefitsHuman gene for Bacteria produce insulin (to Insulin hormone treat diabetic patients) cheaplyinserted into bacteria and in great quantity

Human genes for blood- Sheep can be milked and bloodclotting factors inserted factors extracted to treat into sheep, which produce patients suffering Haemophiliablood factors in theirmilk

Strawberry plants have Allows strawberries to be received a gene from a grown in colder areas notfish, which allows them previously possibleto resist freezing better

Crop plants have received Crops do not need to be a gene from the sprayed with insecticides toPyrethrum plant which control insect pests...causes the crops to any insect which eats the cropproduce a natural will dieinsecticide chemical

How Genes are TransferredThe exact mechanism of transfer depends on the species.

Firstly, the gene to be transferred from the “source species”needs to be isolated. This is often achieved by collectingDNA from cells of this species and chopping it intofragments using “restriction enzymes” from bacteria. Theseenzymes have the ability to cut DNA into sections. It oftentakes a lot of trial-and-error to then locate a fragment ofthe chopped-up DNA containing the desired gene.

The desired fragment can then be incorporated into theDNA of the “target species” by several possible methods.

• In some cases the DNA fragment can be injected into an eggof the target species. The DNA becomes incorporated into achromosome and is an inherited gene from that point on.

• Some viruses quite naturally transfer pieces of DNA fromone cell to another. These can be “enlisted” as vectors tocarry DNA to the target cells. The DNA fragment isinserted into a harmless virus. Then when the virus isallowed to infect a “target cell”, the DNA fragmentbecomes incorporated into its chromosomes.

• In the case of transferring human genes into bacteria, thesame “restriction enzyme” is used to chop-up both thehuman DNA, and the bacterial “Plasmid”... a bacterialchromosome. Since both were cut by the same enzyme, thefragments match-up, and can readily join together whenmixed in the presence of suitable enzymes. This techniquehas been in use for about 40 years, notably to produce purehuman insulin for treating diabetics.

Ethical Issues Concerning Transgenic Species

While Reproductive Technologies may cause somescientific concerns about loss of genetic diversity, the mainconcerns about Transgenic species tend to be ethical.

You need to be aware of the issues and prepared to formyour own, informed opinion... there is no single correctanswer.

Weigh up the benefits (some listed in table at left) againstthe concerns some people raise...

• transferring genes, especially human genes, into otherspecies is unnatural, and wrong religiously and morally.

• foods from transgenic species may have unforseenconsequences for human health, such as inceases in cancer.No-one has the right to expose us all to unknown risks.

• under current law, the companies who develop transgenicspecies own patents on them, and are making huge profitsby forcing farmers to use their products or sell-out.This is seen as unethical, putting profit before people.






29

CONCEPT DIAGRAM (“Mind Map”) OF TOPICSome students find that memorizing the OUTLINE of a topic

helps them learn and remember the concepts and important facts.Practise on this blank version.

THE BLUEPRINTOF

LIFE

Practice QuestionsThese are not intended to be "HSC style" questions, but tochallenge your basic knowledge and understanding of thetopic, and remind you of what you NEED to know at theK.I.S.S. principle level.

When you have confidently mastered this level, it is stronglyrecommended you work on questions from past exampapers.

Part A Multiple Choice1.The fossil record shows a pattern, from ancient times torecent times, of:A. more complexity to less complexity.B. greater diversity to less diversity.C. increasing complexity and diversity.D. no distinct pattern of change.

2.The famous fossil “archaeopteryx” is best described as a:A. common fossil, found in many rock layers.B. “transitional form”, showing a stage of evolution.C. “index fossil”, useful for correlating between locations.D. “living fossil”; an extremely primitive bird alive today..

3.Two types of evidence which suggest descent from acommon ancestor are:A. embryos of vertebrates and the pentadactyl limb.B. convergent evolution and comparative biochemistry.C. DNA structure and the biogeography of grazers.D. natural selection and survival of the fittest.

4.“Natural Selection” refers toA. those organisms best suited to the environment survive

and reproduce.B. factors of the environment determining which

organisms survive and which do not.C. the changes to living things over many generations.D. the way that not all organisms can survive because too

many offspring are produced.

5.The really important part of “Survival of the Fittest” is:A. being very well adapted to the environment.B. living a long and healthy life.C. being “chosen” by the environment to survive.D. reproducing many offspring.

6.A species has a better chance of long-term survival duringchanges to the environment if:A. it reproduces asexually.B. most individuals are similarly adapted.C. the species has a lot of variation and genetic diversity .D. there are many large, strong individuals in the group.

7.An example of “microevolution” that has actually beenobserved to happen, is:A. the extinction of the dodo.B. divergence of “Darwin’s finches” on the Galapagos

Islands.C. convergence of the shark and dolphin.D. change in the population of the “Pepper Moth”.

8.When Gregor Mendel crossed pure-breeding tall pea plantswith pure-breeding dwarf plants, and bred them through 2generations, he found that the F2 phenotypes were:A. 100% tall plantsB. 75% tall: 25% dwarf, approximately.C. 50% tall : 50% dwarf, approx.D. ratio of 3:1, dwarf : tall, approx.

9.The genotype of a pea plant described as “heterozygoustall” would be:A. Tt B. T C. TT D. tt

10.In mice, Black coat (B) is dominant to white (b). If aheterozygous mouse mated with a white mouse, you wouldexpectA. approximately 75% of the babies to be black.B. all the babies to be black.C. approximately 50% of the babies to be whiteD. all the babies to be white.

11.The following pedigree shows the inheritance of “toothgap” (a gap between the 2 top-front teeth) in a humanfamily. Shaded shapes show people with a tooth gap.

It would be true to say that:A. “tooth gap” is dominant because it’s more common.B. couple 3 & 4 are both heterozygous for this trait.C. the exact genotypes of 10 & 11 are uncertain.D. individual 9 must be homozygous.

30




11

55

22 33 44

66 77 88 99

11111100

I

II

III

12. A pair of homologous chromosomes:A. are identical to each other.B. carry totally different genes C. will line up as a pair during mitosis.D. carry alleles in corresponding locations.

13. Meiosis produces:A. 4 haploid gamete cells.B. 2 diploid body cells.C. 4 identical gametes.D. 4 non-identical body cells.

14. A “nucleotide” contains:A. sugar, phosphate and one of 4 possible “bases”.B. a “base”, phosphate, and one of 4 possible sugarsC. amino acids in a polypeptide chain.D. base pairs A-T and C-G.

15. In human sperm cells you would expect to find:A. 46 chromosomes including an Xy pair.B. 46 chromosomes including either an X or a y.C. 23 chromosomes, including an X.D. 23 chromosomes, including either an X or a y.

16. If a recessive gene is “sex-linked” you would expect:A. males and females to show the phenotype equally.B. a heterozygous female will show the recessive phenotype.C. males may inherit the trait only from their mother.D. males will pass the recessive gene on to their sons.

17.In a species of small African rodents it was noticed that 2grey coloured animals produced a litter of babies that wereabout 25% white, 25% black and about 50% grey. It seemslikely that:A. grey is dominant to both black and white.B. co-dominant alleles are controlling coat colour.C. a mutation occurred to produce new colours in thebabies.D. grey is a recessive gene, black and white are co-dominant.

18.Which of the following is NOT a source of increasedgenetic diversity in a species?A. Mutation in a gamete before fertilization.B. Crossing-over process during mitosis.C. Independent segregation of homologous pairs inmeiosis.D. Combining gametes from different parents atfertilization.

19.DNA replication is possible because:A. DNA acts as a template to make m-RNA.B. Each DNA strand makes an identical copy of itself.C. Each DNA strand makes a complementary strand.D. The polypeptide chains in DNA are “mirror images”.

20.The factor least likely to be mutagenic is:A. nuclear radiation.B. herbicide chemicals like agent orange.C. ultra-violet light.D. low temperatures.

21.The base sequence on a part of a DNA chain is

...ATTCGAGGCTAC...Which of the following statements is correct?A. This section could code for 4 amino acids.B. The complementary strand would read

TAACGACCGTAC.C. This section contains 6 codons.D. The corresponding m-RNA section would be

ATTCGAGGCTAC.

22.When genes are transferred from one species to another:A. this reduces the genetic diversity of the species.B. this is a mutation.C. this produces a transgenic species.D. the result would be a clone of the original.

Part B Longer Response QuestionsMark values given are suggestions only, and are to give you an ideaof how detailed an answer is appropriate.

23. (4 marks) Explain the difference between “relative dating” of fossilsand “absolute dating”, by outlining how each is achievedand what each can tell you about fossils.

24. (3 marks)Comparative Anatomy can give evidence supporting theidea of evolution.a) Outline an example of comparative anatomy that givessuch evidence.b) State how this example is evidence of evolution.

25. ( 3marks)Briefly discuss, using an example, how advances intechnology have changed scientific thinking aboutevolutionary relationships.

26. (5 marks)Outline the Darwin-Wallace Theory of Evolution.

27. (4 marks)Differentiate between “convergent” and “divergent”evolution, giving examples of each.

31




28. (6 marks)Explain the difference between each pair of words:a) Dominant & Recessive genes.b) Homozygous & heterozygous.c) Genotype & Phenotype.

29. (5 marks)Outline the reasons why:a) Mendel’s experiments were successful in discovering thefundamentals of how inheritance works.

b) Mendel’s discoveries were ignored by other scientists formany years.

30. (5 marks)In pea plants, green seed pods(G) is dominant to yellowpods (g).A pure breeding green pod plant was crossed with a pure-breeding yellow pod plant.a) Explain why all the offspring will have green pods.

b) One of these offspring plants was later crossed with ayellow pod plant. Showing all working, predict thephenotypes (as ratio or percentage) of the offspring fromthis second cross.

31. (8 marks)a) Use the following information to construct a pedigreediagram.

Inheritance of red-hair in the Meggs family.Fred and Mary both have blonde-brown hair. They have 4children, a daughter and 3 sons. Their daughter and one sonare red-heads, the other 2 sons are similar to their parents.The red-headed son married a red-headed girl and theyhave a son and a daughter.

b) State whether “red-headedness” is a dominant orrecessive trait, giving reason(s).

c) Predict the hair colour of Fred & Mary’s grandchildren.Explain your answer.

32. (6 marks)a) Sketch one pair of homologous chromosomes, justbefore a cell was to undergo a cell division.If the organism is heterozygous for allelic genes “Q” and“q”, show on your diagram the positions of all copies ofthese genes.

b) Draw simple sketches to show:i) how these 2 chromosomes would line up for mitosis.ii) the chromosomes in ONE of the cells resulting from

mitosis.iii) how these 2 chromosomes would line up for meiosis.ii) the chromosomes in ONE of the cells resulting from

meiosis.

33. (5 marks)In Drosophila fruit flies, the normal eye colour is red. Arecessive, sex-linked gene causes white eyes.Using symbols XR, Xr and y, predict the phenotypes(separately for each sex) of the cross between a white-eyemale and a heterozygous red-eye female. Show yourworking.

34. (5 marks)A certain species of African rodent was described inMultiple Choice Question 17.Using appropriate (declared) symbols, predict the outcomeof a mating between a grey and black animal of thisspecies.

35. (3 marks)a) Explain, with the help of simple diagrams if you wish,the process of “crossing over” with chromosomes.

b) Explain how this process contributes to the geneticdiversity of a species.

c) State one other process which increases genetic diversityin a species.

36. (6 marks)Use a simple flow chart diagram to outline the process bywhich DNA controls the production of a polypeptide.

37. (5 marks)a) What is a “mutagen”?

b) Describe 2 pieces of evidence that radiation ismutagenic.

c) Describe using a simple flow chart, how a change in aDNA sequence could result in a change in cell activity.

38. (4 marks)Compare and contrast the idea of “Gradualism” inEvolution, with the theory of “Punctuated Equilibrium”.

39. (5 marks)a) Outline the process that can be used to make a clone ofa mammal.

b) Explain the effect that cloning could have on the geneticdiversity of the cloned species.

40. (5 marks)a) Give an example of the use of a “transgenic” species,stating:

i) precisely which species are involved, andii) the benefit or purpose achieved.

b) State an ethical concern that some people might havewith the use of this transgenic species.

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33

Worksheet 2Part Aa) Mendel b) peac) inherited d) puree) pure-breeding f) dwarfg) F1 h) talli) self j) 2nd generationk) 3:1 l) genesm) alleles n) allelico) 2 p) the sameq) heterozygous r) gametess) fertilization t) parentu) recessive v) dominantw) homozygous x) phenotypey) actual genes present. z) simple, easily identifiedaa) pure-breeding ab) largeac) statistically ad) a recognised scientistae) German

Part B1. a) i) green ii) yellow iii) green

b) i) GG ii) Gg iii) ggc)i)

Answers only for the rest of these.ii) Gg x GG: 100% greeniii) gg x GG 100% greeniv) Gg x gg 50% green : 50% yellow

2. a) i) BB x bb: all offspring will have genotype Bbii) Phenotype: all will be black

b) i)

ii)Not surprizing.In such smallsamples, randomchance can giveresults not exactlyin the expectedratio.

Gg Gg

G & g G & g

G g

G

g Gg

GG

gg

Gg

x

gametes

PPhheennoottyyppeess ooff OOffffsspprriinnggGGrreeeenn :: YYeellllooww

33 :: 117755%% :: 2255%%

Bb bb

B & b b & b

b b

B

b bb

Bb

bb

Bb

x

gametes

PPhheennoottyyppeess ooff OOffffsspprriinnggBBllaacckk :: AAllbbiinnoo

5500%% :: 5500%%

Answer Section

Worksheet 1Part Aa) Palaeontology b) fossilsc) less d) moree) less f) moreg) present-day organisms h) millions (billions)i) relative j) correlatingk) Radiometric l) transitionalm) Archaeopteryx n) dinosauro) bird p) how living things are distributedq) very similar r) very differents) common ancestor t) bone structureu) for different purposes v) Pentadactyl limbw) DNA x) enzymesy) common ancestry z) species can be changed

Part Ba) Charles Darwin & Alfred Wallaceb) more offspring than can possibly survivec) variation (genetic diversity)d) Natural Selectione) best suited f) reproduce / breedg) Survival of the Fittest h) evolves / changesi) predators, food, supply j) who are best suitedk) reproduce l) survivem) reproduce n) Peppero) industrial p) black to light mothsq) DDT r) selections) resistant t) extinctu) Partitioning v) using slightly different resourcesw) evolves into several / more than onex) isolated y) selectionz) Convergent aa) resembleab) similar / same ac) characteristics / adaptationsad) dolphin ae) features / adaptationsaf) closely related




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Worksheet 3Part B continued1. d) ii) Females 100% Red-eyed. Males 100% white eyed.

2. a) XNXN b) XNy c) Xnyd) XnXn e) XNXn

f)

3.a)

b) WW x RW. Phenotypes of offspring 50%White, 50% Roan.

4.a)

b) BB x WW gives 100% Speckled offspring.c) BB x BW gives 50% Black and 50% Speckled.

XNNy XnnXnn

XNN & y Xnn & Xnn

Xnn Xnn

XNN

y Xnny

XNNXnn

Xnny

XNNXnn

x

gametes

PPhheennoottyyppeess ooff OOffffsspprriinnggFFEEMMAALLEESS MMAALLEESS

110000%% nnoorrmmaall 110000%% ccoolloouurr bblliinnddvviissiioonn

RW RR

R & W R & R

R R

R

W RW

RR

RW

RR

x

gametes

PPhheennoottyyppeess ooff OOffffsspprriinnggRReedd :: RRooaann

11 :: 115500%% :: 5500%%

BW BW

B & W B & W

B W

B

W BW

BB

WW

BW

x

gametes

PPhheennoottyyppeess ooff OOffffsspprriinnggBBllaacckk :: SSppeecckklleedd :: WWhhiittee

11 :: 22 :: 112255%% :: 5500%% :: 2255%%

3. a) Recessive. Couple 7 & 8 have straight fingers, but had a child(11) with curved little fingers. This can only happen if both parentsare carrying a “hidden” gene... therefore it must be recessive.b) S = Straight, s = curved.c) 1=ss, 2=SS, 3=ss, 4=SS, 5=Ss, 6=Ss, 7=Ss, 8=Ss, 9=Ss,10=SS or Ss(uncertain), 11=ssd) No chance of curved-finger children, because all children mustreceive a “S” gene from mother who is “SS”.e) Ss x ss would give 50% curved, 50% straight.f) It is quite possible. Prediction is not wrong.In small samples, random chance can result in offspring ratios thatare not in agreement with the prediction. (In a large sample ofoffspring there should be approximately 50-50)

Worksheet 3Part Aa) nucleus b) cell divisionc) homologous d) allelice) replicated / duplicated f) chromatidsg) identical h) in single filei) chromatids j) identicalk) parent l) in pairsm) homologous n) 4o) half p) diploidq) haploid r) 46s) 23 t) Sutton & Boveriu) chromosomes v) meiosisw) the genes must be located on the chromosomesx) DNA and protein y) genez) DNA aa) polymerab) nucleotides ac) sugar, phosphate & basead) A,C,G & T ae) helixaf) 2 ag) A-T and C-Gah) genes from 2 different parentsai) Independent Segregation aj) Crossing-over

Part B1. a) Males cannot be heterozygous because they only have one Xchromosome. The y chromosome doesn’t carry an allele.b) From his mother, who gives him his X chromosome. Fathergives y, which doesn’t carry an allele.c) i) XRXr ii) Red-eyediii) She carries the recessive gene and passes it to her children, butdoes not show the phenotype of it herself.

d) i) Xrry XRRXrr

Xrr & y XRR & Xrr

XRR Xrr

Xrr

y XRRy

XRRXrr

Xrry

XrrXrr

x

gametes

PPhheennoottyyppeess ooff OOffffsspprriinngg FFEEMMAALLEESS MMAALLEESS

RReedd::WWhhiittee RReedd :: WWhhiittee5500%% :: 5500%% 5500%% :: 5500%%




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Practice QuestionsPart A Multiple Choice1. C 5. D 9. A 13. A 17. B 21. A2. B 6. C 10. C 14. A 18. B 22. C3. A 7. D 11. B 15. D 19. C4. B 8. B 12. D 16. C 20. D

Part B Longer ResponseIn some cases there may be more than one correct answer possible. The following “model”answers are correct, but not necessarily perfect.

23. Relative Dating is done by correlating fossils from one placewith those elsewhere. It allows scientists to put things in order,from oldest to youngest, but the actual ages cannot bedetermined.Absolute Dating involves measuring the radiation from naturallyoccurring radio-isotopes. These “decay” at known rates, so theamount of radiation remaining in a rock or fossil allows the actualage in years to be determined.

24. a) An example is the “Pentadactyl Limb” structure invertebrate animals. The bone structures in the fore-limb of awhale, bat, dog, human, lizard, etc. are all essentially the same,even though each looks very different on the outside, and each isused for very different purposes... swimming, flying, walking, etc.b) This is evidence of descent from a common ancestor whichhad that bone structure.

25. Sequencing the DNA of different species allows their degreeof “relatedness” to be determined very precisely, since closelyrelated species have very similar DNA.This has revealed some surprizes that have changed the thinkingon evolutionary relationships. For example, it has previously beenthought that lizards and crocodiles (both classified as reptiles) aremore closely related to each other than to birds. DNA analysisreveals that birds are more closely related to crocodiles than eitheris to the lizards.

26. (Best in 5 numbered points)1. All species produce more offspring than can survive.2. There is variation within each species... not all the same.3. “Natural Selection”: the factors of the environment choosewhich individuals survive.4. “Survival of the Fittest”: those best suited to the environmentsurvive and reproduce.5. The “survival characteristics” get passed on to offspring soeach generation is slightly different than before. Over manygenerations the species changes... it evolves.

27. Divergent evolution is when one ancestral species evolves into 2or more different species. An example is the finches of theGalapagos islands, where a different species of finch has evolved oneach separate island, all from a single ancestral species.Convergent evolution is when different species evolve to resembleeach other, even though they are not closely related. An example isthe shark & dolphin which are both streamlined, fast-swimminglook-alikes, but are not related in an evolutionary sense.

28. a) Dominant gene will always be expressed.Recessive gene can only be expressed when no other allele is present(i.e. if homozygous for the recessive gene)

5. a) If the 2 alleles are Codominant, then there can be 3phenotypes.b) Best to use 2 different CAPITAL letters, R & W.c) i) RR ii) RW iii) WWd)

Parents: RR x WWGametes: R only W only

F1: 100% RW (Pink)

F2

Worksheet 4a) communication b) collaborationc) Wilkins d) Frankline) Watson f) Crickg) base h) doublei) replicated j) divisionk) unzip / untwist l) templatem) A & T n) C & Go) identical p) amino acidsq) polypeptide r) 3-D shapes) sequence t) 20u) repel v) enzymesw) structural x) shapey) amino z) DNAaa) 3 ab) codonac) Transcription ad) m-RNAae) template af) singleag) sugar ah) baseai) nucleus aj) mitochondriaak) synthesis al) Translationam) polypeptide an) t-RNAao) mitochondria ap) proteinaq) catalyses ar) pigmentas) change at) mutationau) mutagens av) temperatureaw) chemicals ax) X-raysay) nuclear radiation az) Ultra-violet U.V.ba) DNA bb) aminobc) polypeptide bd) shapebe) enzyme bf) pigmentbg) Evolution bh) variation / genetic diversitybi) Punctuated Equilibrium bj) remain unchangedbk) rapid bursts

RW RW

R & W R & W

R W

R

W RW

RR

WW

RW

x

gametes

PPhheennoottyyppeess ooff OOffffsspprriinnggRReedd :: PPiinnkk :: WWhhiittee11 :: 22 :: 11

2255%% :: 5500%% :: 2255%%




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32. a)

b)

33.

34. Gene symbols: B= Black, W=White

QQ QQ qq qq

HHoommoollooggoouuss ppaaiirr ooffDDoouubbllee cchhrroommoossoommeess

i) in a single line ii)

iii) in pairsiv)

Xrry XRRXrr

Xrr & y XRR & Xrr

XRR Xrr

Xrr

y XRRy

XRRXrr

Xrry

XrrXrr

x

gametes

PPhheennoottyyppeess ooff OOffffsspprriinnggFFEEMMAALLEESS MMAALLEESSRReedd :: WWhhiittee RReedd :: WWhhiittee5500%% :: 5500%% 5500%% :: 5500%%

BW BB

B & W B & B

B B

B

W BW

BB

BW

BB

x

gametes

PPhheennoottyyppeess ooff OOffffsspprriinnggBBllaacckk :: GGrreeyy

11 :: 115500%% :: 5500%%

GREY BLACK

b) Homozygous means having 2 copies of the same allele for aparticular trait. eg, AA, or bb.Heterozygous means to have 2 different alleles for the trait. eg, Aac) Genotype is the description (usually in symbols) of the actualgenes present for a trait. eg “Aa”.Phenotype is the outward appearance caused by the genes for thattrait. eg “Purple flowers” or “Dwarf stem”.

29. a) Mendel’s experiments were successful because:• he chose to study simple traits that occurred in just 2 alternativeforms, such as Tall v. Dwarf.• he began with pure-breeding parent plants.• he bred large numbers of offspring so the results could beinterpreted statistically.b) His work was ignored because:• he was not a recognised scientist, but a monk in an obscuremonastery.• his findings were published in a little-known journal, in German,so were not read by many people (and those that did, didn’t realizethe significance).

30. a) Each of the offspring will receive a gene from each parent andso all will have genotype “Gg”. Since G is dominant, it will beexpressed (= green pods), while the recessive “g” gene will have noeffect.b)

31. a)Shaded shapes are red-heads

b) Red-headedness must be recessive, because Fred & Mary are notred-heads, but had red-headed children. They must both carry arecessive gene.c) Must both be red-heads, since their parents are. Since it’s recessive,both 6 & 7 must be homozygous for red-hair and must pass ongenes to children 8 & 9, who also must be homozygous.

Gg gg

G & g g & g

g g

G

g gg

Gg

gg

Gg

x

gametes

PPhheennoottyyppeess ooff OOffffsspprriinnggGGrreeeenn ppoodd :: YYeellllooww ppoodd

11 :: 115500%% :: 5500%%

FFrreedd

55

MMaarryy

33 44 66 77

88 99

I

II

III

GGeenneerraattiioonnss



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38.Similarity: both are models describing evolution of a species.Difference:“Gradualism” = evolution occurring slowly and steadily overrelatively long time periods.“Punctuated Equilibrium” = species remains unchanged for longperiods, then evolves in a rapid burst.

39.a) • Body cell taken from “parent”, and nucleus extracted.• Egg cell obtained and nucleus replaced with nucleus from“parent” cell.• Egg cell implanted in uterus of surrogate mother, wherenormal pregnancy and birth occur. Baby is clone of “parent”individual.b) If used on a large scale, cloning would reduce geneticdiversity because less parents are involved and more offspringwould be identical.

40.a) i) Gene from a fish transferred into strawberry plants.

ii) Makes strawberries frost-resistant, allowing them to begrown in areas not previously possible.b) Some people may be worried about long term health effectsof eating transgenic foods.(In this particular case, vegetarians might see it as unethical thatthe strawberries contain an animal gene.)



35 a) “Crossing-over” is whenhomologous chromosomes exchangecorresponding parts of a chromatidwith each other.

b) This mixes up the combinations ofgenes on each chromatid, and results inmore variety of gene combinations in gametes, and in offspring.c) Mutation / Independent Segregation of homologouschromosomes in meiosis / Receiving genes from 2 differentparents during sexual reproduction.

36.

37. a) Mutagen = something that CAUSES a mutation.b) 1. Controlled experiments have demonstrated that mutationsare caused in plant seeds, insects, etc which are exposed tonuclear radiation or x-rays.

2. There was a large increase in human mutations and geneticabnormalities in Hiroshima after the atomic bomb attack of1945, and the Chernobyl accident in Ukraine 1986.c)

DNA

Polypeptide

m-RRNA

m-RRNA controlssequence ofamino acidsjoined together

TRANSCRIPTION

TRANSLATION

Moves to a Ribosome

AlteredDNA

Alteredm-RRNA

AlteredPolypeptide

AlteredEnzymeccaauusseess ddiiffffeerreennttcchheemmiiccaallpprroodduucctt ttoo ffoorrmm

Change incell’s activity

NOTICE ANY ERRORS?

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