HSC Biology Blue Print of Life

7/22/2019 HSC Biology Blue Print of Life

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9.3BlueprintofLife


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1. Evidence of evolution.


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Evolution through natural selection

The theory of evolution attempts to explain how species have changed from

very simple forms to much more complex organismsBoth Darwin and Wallaceconcluded that species are not fixed but change overtime

Darwin introduced the idea of evolution through natural select ion .

The mechanism of natural selection is:

Organisms produce many more offspring than are needed

Due to natural variation the offspring will differ from each other in smallways.

Some of these differences will be inheritable and will offer the organismsthat have them a slight advantage over the others.

These organisms will be better fit to survive and reproduce in that habitat.

Their offspring will inherit those traits and, over time, will become more

numerous in the population.A number of these gradual changes will make the new organismssufficiently different from the original that they can no longer produceviable offspring, should they mate. At this stage they can be considered anew species.


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A model of natural selection

For this experiment you will need a number (20-30)toothpicks which have been dyed three or fourdifferent colours (not real bright ones)

You will need to work in pairs. One of you will be theprey and the other the predator. You will need towork outside in an open area of about 100 sq m.

Record the colour and number of the starting

population.The prey goes outside first and, while the predatorhas their eyes covered up, he/she disseminates the20 toothpicks in strategic areas some where thecolours blend-in and some where they stand out.

Next, the predator is given a fixed time, say 1 minute,to 'hunt' for as many toothpicks as he/she can see

and counts and records the colour and number ofthe victims

The prey goes out again and retrieves all the'survivors'. The survivors are now allowed toreproduce (each colour's number is tripled)

This procedure is repeated a few times (5 or 6) andthen the final population is compared to the startingpopulation.


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Changing conditions

If a species has become adapted to a particular habitat there will stillbe many variations in its population. If none are particularly favoured,then the species will remain relatively unchanged over time

However, if the conditions in the habitat were to change so that someof the different traits in the population are significantly favoured over

others then the species will change over time.

This change is called becoming adapted to the new environment. Ifnone of the variations are favoured in the new environment and thespecies cannot adapt , then it may become extinct

Conditions on Earth have changed a lot over millions of years and

many more species of organism than are alive today have gone toextinction, it is part of the way life has evolved and space is made fornew species

Changes in the habitat can be Physical, chemical or competitive.


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Effect of physical changes

Physical changes in an environment include changes in climate(temperature, rainfall, humidity, etc), amount of light, materials forshelter (rocks, logs etc), flooding and drought.

An example of this, are the types of plants that we find in Australia, aswe move from a temperate coastal climate to an arid one . Both areas

contain similar species of trees but the ones in an arid environment aremuch better at retaining water and minimizing water losses.

Sometimes the organism changes its habitat because of better foodsupply or to minimize predator encounters or maybe conditions in itsoriginal environment have changed.

An example of this is the evolution of whales: their original ancestorwas a wolf-looking coastal predator, which must have spent more andmore of its time in the water. Over millions of years it evolved into afully aquatic species: its anatomy changed radically because of thephysical differences (buoyancy, streamlining, breathing etc) betweenthe two habitats.


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Effect of chemical changes

Sometimes the changes in anenvironment are related to thechemicals in it, which maybe toxic orharmful or beneficial.

An example of this is the on-going warbetween insects and plants: as a plant

develops an new toxin, the insectsfeeding on it develop resistance to itand the plant has to develop newtoxins.

A more visible example, one that we canobserve happening, is the ability ofinsects or bacteria or rats have tobecome resistant to the poisons wedevelop to exterminate them. It's a warthat they are winning by continuouslyevolving.

As agents of evolution we are breedingsuper-pests!


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Effect of competition

An important concept in evolutionary theory is that ofadaptive radiation.

Adaptive radiation is where a number of species,evolved from a common ancestor, have over timesuccessfully adapted to new niches in theirenvironment (via natural selection).

When Charles Darwin visited the Galapagos islands, he

noticed the wide variety of finches that existed on eachof the islands.

Originally, the finches occupied the South Americanmainland as ground-dwelling seed-eaters. Somehowthey managed to colonise the Galapagos islands, over600 miles away.

At first they occupied the new habitat with littlecompetition. But, as the population began to flourish,

resources on the islands were squeezed and would nothave sustained the population for long.

As competition grew, the finches managed to find newecological niches, by adapting to new food sources.They evolved away from the original ancestor changingbeak shapes, feeding habits, plumage etc.

The finches had adapted to their environment via

natural selection, due to a competition for resources


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Evidence for Evolution

Since the time when Darwin and Wallace published their theory ofevolution, a lot of evidence supporting the theory has been obtained.The amount of evidence is much too great to deal in here, but a fewimportant examples follow.

It is important to note that he evidence does not come from one area ofscience alone, but it comes from a number of diverse fields:paleontology; anatomy; embryology; bio-geography and biochemistry.

Little or no evidence has been found for the competing theories ofLamarkism, Creationism (in a short time span); Spontaneousgeneration or Intelligent Design.

Some of the evidence for evolutionary theory may point at different

mechanisms than those suggested by Darwin (e.g. punctuatedequilibrium) but none of the evidence, to date, has contradicted thebasic theory.


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PaleontologyThis type of evidence is based on theextensive fossil record that has been leftbehind by previously living organisms.

A careful study of fossils highlights asteady increase in the complexity oforganisms. The gradual development ofspecialized morphology is clearlyillustrated in countless examples.

A very good example of this gradualchange is the evolution of horses .

Fossils that are on the cusp of a majormorphological change are known ast ransit ional forms.

A very familiar example of a transitionalform are the fossils ofarchaeopteryx. Theyclearly show some reptilian and some bird-

like structures, all in the same animal.Could monotremes, the Australian egglaying mammals, be living transitionalforms between mammals and egg layingreptiles?


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Comparative Anatomy(homology)

Comparing the anatomy of similarorganism often highlights body parts thatare similar in structure and function,suggesting a common ancestor.

A good example is the vertebrate limb.

The similarity in bone structure is evidentin the vertebrate limbs shown here

This example is often referred to as'homologou s st ructures in the ver tebratepentadactyl l imb '

Similar studies of other homologous

structures in other classes of organismsyield the similar results: commonancestors (e.g. wings in insects)

The concept of common ancestorship isone of the main concepts in Darwin'sTheory of Evolution .


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Vertebrate limbs

Print this slide

Identify theforelimbs and hindlimbs in each of

the skeletonsshown

Colour-in thehomologousstructures on themusing the samecolours

Deduce reasons

why they aresimilar and whythey are differentfrom each other.


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Comparative Embryology

Embryology is the study of thedevelopmental stages of anorganism from fertilized egg tobirth.

A comparison of vertebrateembryos illustrates their strongrelationship and developmentalsimilarity. Early-on in theirdevelopment, an expert biologistwould be required to distinguishbetween them.

For example, they all go througha stage where vestigial tails andgills are present. Eventually, theydevelop into different structuresdepending on the speciesconcerned (e.g. gills becomeears in human embryos).


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Bio-geography

Bio-geography deals with how organisms, that can be shown to share a

common ancestry, differ from each other because they have occupieddifferent habitats.

The finches of the Galapagos Islands are an obvious example of bio-geographical evidence, as they show significant differences amongthemselves and with the mainland South American finches.

The evolution of Australian macropods('big-feet': kangaroos and wallabies)

can also be related to bio-geography. The common ancestor (about 25 mya) ofall macropods is thought to have been an ancient tree-dwelling marsupial(Balbar idae).

With the continent becoming more and more arid macropods evolved andadapted to different energy-poor habitats where food was sparse and thelandscape had less and less suitable trees. Some had to evolve an extremelyefficient way of covering large distances - hopping to it!.


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Convergentevolution

Convergent evolution is a term that isused to describe the evolution ofrelatively unrelated species intosimilar organisms that have similarstructures, physiology and/orbehaviours

This parallel evolution is in responseto similar environments.

The organisms may not only havequite different ancestry but may alsolive in completely different times andmay have evolved in different epochs,

but because the habitat conditionswere very similar, the evolutionarysolution to survival was similar.

Adjacent are some notable examples.


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A case study-environmental

change

Koala fossils are quite rare, but some have been found in northern Australiadating back to 20 million years ago.

During this time, the northern half of Australia was rain forest. The Koala'sancestors did not specialize in a diet of eucalyptus until the climate cooled anddried, eucalyptus forests replaced rain forests.

Its origins are still unclear, however, since its pouch opens backwards insteadof forwards as would be expected in a tree-climbing marsupial. It has beentheorised that Koalas may have evolved from a burrowing marsupial.

The thinning of the forest probably made the koala an easier prey forcarnivores like the marsupial lion (Thyl acaleo Carnifex) which lived up to200,000 years ago. The koala survived predation by adapting to an entirelyarboreal existence.

The species also shifted its distribution further south in the continent,following locations where eucalypts were the dominant plant species.


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Revision questions- 1

1) Outline the impact on the evolution of plants and animals of: changes in physical conditions inthe environment; changes in chemical conditions in the environment and competition forresources

2) Describe, using specific examples, how the theory of evolution is supported by the followingareas of study: paleontology ( including fossils that have been considered as transitionalforms); bio-geography; comparative embryology; comparative anatomy and biochemistry

3) Explain how the Darwin / Wallaces theory of evolution by natural selection and isolationaccounts for divergent evolution and convergent evolution

4) Describe a first-hand investigation you performed to model natural selection

5) Describe using a named example how an environmental change can lead to changes in aspecies

6) Describe a first-hand investigation you performed to observe, analyse and compare the

structure of a range of vertebrate forelimbs

7) Analyse, using a named example, how advances in technology have changed scientificthinking about evolutionary relationships

8) Assess social and political influences on the historical development of theories of evolution


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Mendel's workExperiments on Plant Hybridisat ion was presented in 1865 by Gregor Mendel at twomeetings of the Natural History So ciety of B rnn, in Moravia. It was the result of morethan 29 000 experiments and 11 years of studying genetic traits in pea plants.

Mendel compared seven discrete characters of pea plants in his study of inheritedcharacteristics:

Colour and smoothness of the seeds (grey and round or white and wrinkled)

Colour of the cotyledons (yellow or green)

Colour of the flowers (white or violet)

Shape of the pods (full or constricted)

Colour of unripe pods (yellow or green)Position of flowers and pods on the stems (terminal or axial)

Height of the plants (short ~1 ft or tall ~ 6 ft)

In 1866 Mendel published his work on heredity in a little known journal (Proceedings ofthe Natural History Society of Brnn or Verhandlu ngen des naturfo rschend en Vereins

Brnn). Not surprisingly, it had little or no impact.

His ideas and findings were revolutionary but his writing style was tedious, complex and

detailed it was not understood even by influential people in his field . He did make someattempt to contact scientists abroad by sending them reprints of his work but this was anuphill struggle for an unknown author, writing in an unknown journal, in a difficultlanguage.

It was not until 1900 that his work was 'rediscovered' by de Vries and Correns. But, itwas not until the early 1920's that the full significance of his work was recognised, inparticular, its significance to evolutionary theory.


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Mendel's genius - 2Mendel began by ensuring his plants were all 'true-breeding' plants(homozygous).

As a botanist he knew that he must control fertilization

Self -fer ti l izat ion w as con trol led by c over ing th e f lowers to m ake sure theirpol len (f rom the stamens) landed on the st igm a of the same f lower.

Control led cros s-fer t i l izat ion was ensured by c ut t ing o f f the stamen from a

f lower before pol len was p roduced, then d ust ing the st igma of the f lower

with p ol len from the plant he intended to us e.Cross co ntamination f rom other f lowers was st r ic t ly avoided

He let the plants self-fertilize to produce offspring identical to the parentsnumerous times.

Mendel cross-fertilized two true-breeding plants for one trait. Then he allowedthe offspring to self fertilize or cross-fertilize producing second and third

generations.

In each case, he found that the first generation always showed the phenotypeof one of the parents, he called this a dominant trait and the other a recessivetrait. Further fertilization experiments always produced the same simple ratiosof traits, now known as Mendelian ratios or as Mendelian inheritance.


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Hybridisation

In biology, hybrid has two meanings. In the first meaning,a hybrid is the result of interbreeding between twoorganisms of different species within the same genus.These hybrids are often sterile (e.g. the mule and thehinny are sterile hybrids of breeding horses withdonkeys).

In this second meaning, a hybrid refers to hybridisation

within a species and between different breeds or strains. Itis used in plant and animal breeding. (e.g. breeds of catsand dogs, farm animals, crops)

In these cases, hybrids are commonly produced andselected because they have desirable characteristics ofboth parents. Most agricultural animals and plants are theresult of hybridisation.

Sterile hybrids would be a negative in a crop such aswheat (growing a crop which produces no seeds would bepointless), but it is an attractive attribute in some fruits.

Bananas, seedless watermelon, seedless grapes forinstance, are intentionally bred to be sterile so that theywill produce no seeds making them easier and more

pleasant to eat.

Example: WarmbloodHorsesA warmblood ho rse is theresul t of hyb r id isat ionbetween pure-bloodedhorses such as Engl ishthoroughbreds and heavierfarm horses to produce a

hors e for a specif icfunct ion and purpose suchas show- jump ing ordressage. Careful b reedingprog rams are carr ied out toprod uce a horse ideallysuited to th e breeders'needs.


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3. Chromosomes


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ChromosomesMitosis and meiosis were discovered in theearly 20th Century. At that time it was alsorealised that the nucleus of the cell containedthe material responsible for inheritance.

In 1903 Walter Sutton (1877-1916) andTheodore Boveri (1862-1915) while studyinggamete formation (independently) concluded

that it was the chromosomes that carried theinheritance material.

They noticed that in normal body cellschromosomes came in pairs, but that ingametes they were no longer in pairs.

This led to the "Chromosomal Theory ofInheritance," which states that chromosomescarry hereditary units, and that the sperm andegg have half the number of chromosomesfound in the typical cells of the resultingoffspring.

The chromosome


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The chromosomeWhen the cell is not in the process of dividing chromosomes are invisible.

Just prior to cell division, the DNA in chromosomes becomes more tightly packed and thechromosomes become visible under a light microscope.

When they are stained with special dyes they become 'banded (the banding is used torecognise each individual chromosome).

Chromosomes are made of about 40% DNA and 60% DNA-bound proteins, which serve topackage the DNA and control its functions. The word chromosome comes from the Greekchroma (color) and soma (body) due to their property of being very strongly stained byparticular dyes.

In eukaryotes, DNA is packaged by proteins into a condensed structure called a chromat in.This allows the very long DNA molecules to fit into the cell nucleus.

Chromosomes may exist as either duplicated or as single chromatins. Duplicatedchromosomes (copied at the start of cell division) contain two copies joined by a centromere.(the classic four-arm structure)

Human cells have 22 different types of autosomes, each present as two copies (diploid), andtwo sex chromosomes (46 in total).

The DNA in a chromosome is divided into: functional (coding DNA) and non-functional (non-coding DNA) .

A gene is a region of functional DNA that controls the base sequence used in the production ofa specific polypeptide or RNA.

A human chromosomes may contain from 500 genes (Y chromosome)to more than 4000genes (chromo some 1). A gene can be as short as 1000 nucleotides to as long as severalhundred thousand nucleotides.

DNA


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DNADeoxyribonucleic acid (DNA) is a polymer madeup ofnucleotide units. Each nucleotide is made

up of aphosphategroup jo ined to a sugarmolecule which is jo ined to anorganicni trog enous (containing Nitrogen) base. Themain role of DNA molecules is the long-termstorage of genetic information.

The backbone of the DNA strand is made fromchemically joined, alternating phosphateandsugarmolecules. The sugar in DNA is a five

carbon sugar: 2-deoxyr ibose. ( the sugarr iboseis found in RNA)

The DNA double helix is held together byhydrogen bonds between the bases attached tothe sugar molecules on each of the two strands.The four bases found in DNA are adenine (A),cytosine (C), guanine (G) and thymine (T) (the

base uracil replaces thymine in RNA).Each one of the four bases can only formhydrogen bonds to its complementary base: Aonly joins with T; G only joins with C(mnemonic: A 'T' on the Golf Course)

It is the sequence of these four bases along thebackbone that is the code for all life on Earth

(some viruses use RNA).


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Sex-linked inheritance

T H Morgan (1866 1945) was an Americangeneticist and embryologist. Following therediscovery of Mendelian inheritance in 1900,Morgan's research moved to the study of mutationin the fruit fly (Drosop hi la melanogaster).

In his famous fly-room at Columbia University,Morgan was able to demonstrate that genes arecarried on chromosomes and that they are themechanical basis of heredity.

in 1910 Morgan noticed that when white-eyed maleflies were bred with a red-eyed female, theirprogeny were all red-eyed, while a secondgeneration cross produced white-eyed males: hehad disco vered sex-l inked inher i tance

In a paper published in Science in 1911, he

concluded that (1) some traits were sex-linked, (2)the trait was probably carried on one of the sexchromosomes, and (3) other genes were probablycarried on specific chromosomes as well.

He was awarded the Nobel prize in 1933 for hiswork in genetics

A sex-linked recessive trait


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A sex-linked recessive traite.g. colour-blindness

C d i


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Codominance

In codominance, neither allele is recessive.Instead, the heterozygous individualexpresses both phenotypes.

A common example is the ABO bloodgroup system. The gene for blood typeshas three alleles A, B and O.

A and B are codominant and form bloodtype AB (both alleles are given capitals). Oblood type is recessive to both A and B.

A codominant genetic disease in humans is1-antitrypsin deficiency,

A roan horse has codominant folliclegenes, expressing individual red and whitefollicles. Roan Shorthorn cattle alsoexpress codominant alleles red and white.

Camellia flowers show codominancebetween red and white alleles. (note: pin kcarnat ions sh ow a dif ferent process c al led

' incomplete domin ance')

Effect of environment


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Effect of environmenton phenotype

The environment may affect the expression of a gene. Mendel was able to getreproducible results with phenotype expression because he ensured identicalgrowing conditions.

Had his tall plants received a different fertilizer regimen than his short plants,his results would not have been as clear cut.

Plants grown in different conditions will develop differently. Identical twins,

separated at birth and brought up in different environments may developdifferently in height, weight and even IQ.

A visible example of the effect of environment on phenotype is the colour ofHydrangeas: blue, pink and purple flowers can grow from the same plant. Asoil that is basic causes the blooms to be pink. If the soil is more acid, then theblooms are blue.

Hydrangeas are easy to grow or purchase already established and could form

the centre of your first hand investigation on the effect of environment onphenotype: Plant 3 plants in 3 different pots, add lime to the soil of one plant,add aluminum sulfate to the soil of another and to the third plant's soil addboth. Make sure each receives the same amount of light and water.


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R i i Q ti 3


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Revision Questions - 3

1) Outline the roles of Sutton and Boveri in identifying the importance of chromosomes2) Describe the chemical nature of chromosomes and genes

3) Describe the structure of DNA

4) Explain the relationship between the structure and behaviour of chromosomes during meiosisand the inheritance of genes

5) Explain the role of gamete formation and sexual reproduction in variability of offspring

6) Describe the inheritance of sex-linked genes, and genes that exhibit co-dominance and explain

why these do not produce simple Mendelian ratios

7) Describe the work of Morgan that led to the identification of sex linkage

8) Explain the relationship between homozygous and heterozygous genotypes and the resultingphenotypes in examples of codominance

9) Outline ways in which the environment may affect the expression of a gene in an individual

10) Describe a model that demonstrates meiosis and the processes of crossing over, segregationof chromosomes and the production of haploid gametes

11) A woman falls pregnant while seeing two men. Her blood type is A, the first man's blood typeis B and the second's is O. The baby's blood type is also O. Show that this does not excludethe first man from being the true father. Under what circumstances would the first mandefinitely not be the father? Explain using Punnett squares.

12) Describe a first-hand investigation you performed to demonstrate the effect of the environmenton phenotype


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4. DNA

Franklin vs. Wilkins & Watson & Crick


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Franklinvs.Wilkins & Watson & CrickPart 1

In 1951 James Watson, a biologist and Francis Crick, a physicist, were working at the Cavendish Lab inCambridge, England on the structure of DNA.

Maurice Wilk ins, a physicist at King's College had, in 1951, taken the first X-ray pictures of DNA. Theselead him to suggest the DNA structure might be a helix

Rosal ind Frankl inwas a 30 year old English chemist who was doing brilliant work in a X-raycrystallography lab in Paris, France in 1951. She was head-hunted by J.T. Randall, Director of King'sCollege biophysics labs, to create an X-ray unit and work on DNA. She arrived at the King's College labalso in 1951.

Randall did not clearly delineate a chain of command. He had hired Franklin as director of the x-RAY lab,

without informing Wilkins, who was away on holidays. On his return the startled Wilkins (a man in aman's wor ld), believed himself to be in charge and Franklin to be a glorified lab assistant!

Franklin, a renown feminist, and just as qualified as Wilkins, did not regard him as her superior. Randall'slack of communication was the main cause of the friction between Wilkins and Franklin and their lack ofcooperation in their research efforts.

Previously, a Swiss chemist (Signer) had isolated some quality DNA, which he gave in a "jelly jar" toWilkins sometime in 1951. But it was given to Franklin by Randall, another cause of resentment.

Franklin discovered that Signer's DNA produced X-ray patterns which indicated 2 forms an A form and

a B form. Franklin's efforts often included X-ray pictures that took over 100 hours of exposure .At a Conference attended by Watson, she suggested that B-DNA was helical. Watson and Crick began atonce to build a model, upon its completion they asked Wilkins and Franklin to view the model. Rosalinddid not hesitate in pointing out that it was completely wrong! (The mod el had the phos phate-sugarbackbon e placed inside the molecule with the bases on the outs ide. As a chem ist, she knew that i t had tobe on outsid e the mo lecule in order to give DNA its hydroph i l ic propert ies).

In May of 1952 Franklin took the famous photograph #51 of the B-form, but she set it aside, spending allher efforts on the A-form pictures because they were contradictory.

Franklin vs. Wilkins & Watson & Crick


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Franklinvs.Wilkins & Watson & CrickPart 2

By 1953, conditions at King's had gotten so unsociable that Franklin decided to leave. She had reconciled

her conflicting data on the A-form and had started to write a series of three draft manuscripts, two of whichincluded a double helical DNA backbone. Two of her manuscripts reached Acta Crystallographica inCopenhagen in March 1953.

Wilkins had been as frustrated by Franklin's lack of 'cooperation'. Unfortunately, Wilkins expressed someof his frustration to his friends Watson and Crick ( they w ere competi tor researchers at CambridgeUniversi ty), maybe naively supplying them with crucial data from Rosalind Franklins work.

When he showed them Rosalinds best DNA photograph (#51), Watson immediately saw its significanceand it was enough to start them on the correct solution to DNA. Wilkins also told them about a reportcontaining a summary of Rosalinds latest findings, including all essential molecular size calculations. The

two 'rogues' managed to obtain a copy from Max Perutz. The report was not confidential, but it wasprivate. Perutz passed the report on to Crick without asking Randall or Franklins permission, and theyused it without her permission or acknowledgement !

Watson and Crick now had all Franklins data which showed that DNA was a multiple helix. Crick, who hadworked on proteins, soon realised that Franklins data implied an anti-parallel double helix.

Upon learning of Watson and Cricks model, Rosalind innocently rewrote her own draft manuscript as asupportive paper to theirs, to be published in the same April 1953 issue of Nature. She never knew that herdata had been so essential to Watson and Crick.

Rosalind's photo #51 was a pivotal moment in the discovery of the double helix. At 37 Rosalind Franklindied of ovarian cancer, probably due to constant exposure to X-rays. Four years later, Francis Crick,James Watson, and Maurice Wilkins shared the Nobel Prize but she was not included (the Nobel Prize isnot awarded posthumously).

Strangely, only Maurice Wilkins, with whom she'd fought for so long, acknowledged her contribution in hisacceptance speech. The other two did not mention her valuable and essential help to their work, eventhough, over the years, she had formed a lasting friendship with Francis Crick and his family.

DNA replication DNA replication


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...DNA replication... DNA replication...

DNA replication is complex, fast andvery accurate. It takes place in three,almost simultaneous, steps:

(1) unzipping and uncoiling

(2) adding nucleotides and

(3) forming the two new backbones

The process is helped by enzymes,proteins and RNA.

The two new strands are formed inopposite directions and replicationoccurs at a number of different points

on the huge molecule at the same time(~30 000 points for h uman DNA )


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Effect of changes in DNA


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Effect of changes in DNA

If just one amino acid in hundreds is in thewrong location, the protein or enzyme willnot be able to fold properly and functionproperly, if at all.

This means that whatever processes theprotein or enzyme is used for will notoccur, or at best will occur less efficiently.i.e. cell function will be affected

For example: sickle cell anemia is causedby glutamate amino acid being substitutedby valine amino acid in the haemoglobinmolecule.

As a result the haemoglobin molecule is nolonger globular in shape but is fibrous. Thered blood cells in sickle-cell anaemia havea different shape, which does not flow

through capillaries very well and painfulcirculation problems arise

On the other hand, people with this diseaseare malaria resistant.

The flow chart shows how this couldhappen if just one base pair is changed onthe coding DNA molecule

Polypeptide synthesis 1


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Polypeptide synthesis -1

Transcription starts as the DNA is "unzipped" by the enzyme helicase. RNApolymerase reads the DNA strand and synthesizes a single strand of m-RNA

This single strand of m-RNA leaves the nucleus through nuclear pores, andmigrates into the cytoplasm.

*Note: In RNA the base Uracil substitutes for Thymine

Polypeptide synthesis 2


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Polypeptide synthesis - 2 Translation is the process of converting the m-RNA codon sequences into an

amino acid polypeptide chain. A ribosome attaches to the m-RNA and starts to code at the START codon

(AUG*).

t-RNA brings the corresponding amino acid (which has an anti-codon thatidentifies the amino acid as the corresponding molecule to a codon) to eachcodon as the ribosome moves down the m-RNA strand.

The synthesis ends when the ribosome reads the STOP (UAA, UAG, or UGA)codon, and the polypeptide chain is released.

Polypeptide protein enzyme ?


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Polypeptide protein enzyme ?

The term peptide refers to the type of chemical bond between adjacentamino acid, poly means many .

Both proteins and enzymes are made of polypeptide chains. Enzymes act asbiological catalyst in metabolic reactions. Proteins can be made up of morethat one polypeptide and are more involved with structure and function e.g.muscle tissue, haemoglobin, hair etc

Beadle and Tatum studied mutations in red bread mould caused by irradiationwith X-rays. They found a mould that was unable to grow unless a specificamino acid was added. They found that a single gene was mutated, whichresulted in the lack of a single enzyme

In this way they demonstrated that genes control metabolic processes. Bycoding for the enzymes necessary for the specific metabolic process.

Beadle and Tatum, who won the Nobel prize for their work, demonstrated that

genes code for specific polypeptides. Hence:1 gene => 1 polypeptide*

*Note: the hum an genome project has since shown that one gene may code for manypolyp eptides, as we have only 20,000 (or so) genes, but th ere are many m ore polyp eptides inthe body.

Mutations


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A mutation is a change to the nucleotide sequence of an organism's DNA. Mostmutations are neutral or repaired quickly or harmful, very few are beneficial to the

organism. Mutations can be caused by chance, by chemicals, by viruses or by radiation.

I f the mutat ion is present in a sex cel l , i t wi l l be passed o n to th e offspr in g as a new

al lele (wh ich may or may not be funct io ning ). Mutat ions in sex cel ls may causemisc arr iages, st i l lb i r ths, co ngenital defects, death in the fi rs t year of l i fe, chromo som al

abnorm al i t ies and cancer in later l i fe.

If the mutation occurs in a somatic cell it will be present in all descendants of that cell(certain mutations can cause the cell to reproduce out of control and thus cause cancer)

In 1927 H J Muller published research showing the genetic effects of radiat ion as amutagen. In 1946 he was awarded the Nobel prize for his findings.

Marie Curie discovered Radium and worked with ionizing radiation, she received theNobel Prizes for both physics and Chemistry but died of radiation induced cancer.Rosalind Franklin co-discoverer of the structure of DNA worked extensively with X-rays.She died of ovarian cancer before she could receive her Nobel prize

Long term studies of the Chernobyl disaster have reported an unusually large number

(1,800) thyroid cancers in children from contaminated areas and in many birth defects.

In the late 50's and early 60's, more than 10,000 children in 46 countries were born withsevere deformities. The Australian obstetrician, William McBride, showed that theunfortunate mutations were caused by a drug called tha l idomideif taken duringpregnancy (it was an effective tranquiliser and painkiller).

A chemical or an agent that causes mutations is known as teratogen

Variation


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Variation

Genetic variation is the basic mechanism of evolutionary change. Mendeliangenetics, the processes that occur during meiosis, the structure and functionof DNA all supply ways through which variation in a species is ensured.

There are three main sources of genetic variation:

Meiosis produces genetic variation by the processes of crossing over andrandom segregation, it has the major effect on variation in a population.

Mutations are changes in the DNA which can result in changes in thealleles of genes and can have a large effect.

Gene flow is the movement of genes from one population to another andcan have a significant effect on genetic variation.

G. L. Stebbins, Jr. (1906 2000) was an American botanist and geneticist whois widely regarded as one of the leading evolutionary biologists of the 20th

century. He summarized the importance of variation:In b r ief , evolut ion is h ere visual ized as pr im ar i ly the resultant of th e interact ion

of environmental var iat ion and th e genetic var iabi l i ty recurr ing in the evolving

populat ion

Natural Some modern examples of observable naturalselection are: the increasing resistance ofbacteria to antibiotics and the resistance of


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selectionbacteria to antibiotics and the resistance ofinsects to insecticides.

Antibiotic resistance is the ability of amicroorganism to survive and reproduce inthe presence antibiotics.

Antibiotic resistance evolves via naturalselection acting upon a random mutation.Once such a gene is generated, bacteria canthen transfer the genetic information betweenindividuals by plasmid exchange.

Staphyloco ccus aureus(Staph infection) isone of the major resistant pathogens. It wasthe first bacterium in which penicillinresistance was found just four years after thedrug started being mass-produced (1947).

MRSA (methicillin-resistant S. aureus) wasfirst detected in Britain in 1961 and is now"quite common" in hospitals (MRSA wasresponsible for 37% of fatal cases of bloodpoisoning in the UK in 1999)

Half of all S. aureusinfections are nowresistant to penicillin, methicillin, tetracyclineand erythromycin.

Punctuated Gradualism (Darwin's suggestion) andpunctuated equilibrium (first suggested In 1972by paleontologists N Eldredge and S Gouldare)


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equilibriumby paleontologists N. Eldredge and S. Gouldare)are two of the ways in which the evolution ofspecies is thought to occur.

It is believed that species with a shorterevolution evolved mostly by punctuatedequilibrium, and those with a longer evolutionevolved mostly by gradualism. Some speciesmay have used both mechanisms at differenttimes.

Gradualism is selection and variation that

happens gradually over a long time. Change isslow, constant, and consistent.

In punctuated equilibrium, change comes inspurts. There is a longer period of time whenthere is little change. Followed by a suddenmajor change .

Darwin saw evolution as being "steady, slow,and continuous". Paleontologists have foundfossils that show gradual change but alsofossils that appear on the scene without anyevidence of gradual change. When dating thefossils, results showed that these large changeshad occurred in a relatively short time

Revision questions - 4


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Revision questions 4

1) Describe the process of DNA replication and explain its significance

2) Outline, using a simple model, the process by which DNA controls the production ofpolypeptides

3) Explain the relationship between proteins and polypeptides

4) Explain how mutations in DNA may lead to the generation of new alleles

5) Discuss evidence for the mutagenic nature of radiation

6) Explain how an understanding of the source of variation in organisms has provided

support for Darwins theory of evolution by natural selection7) Describe the concept of punctuated equilibrium in evolution and how it differs from the

gradual process proposed by Darwin

8) Describe a first-hand investigation you performed to develop a simple model forpolypeptide synthesis

9) Outline the evidence that led to Beadle and Tatums one gene one protein hypothesisand to explain why this was altered to the one gene one polypeptide hypothesis

10) Construct a flow chart that shows that changes in DNA sequences can result in changesin cell activity

11) Explain a modern example of natural selection

12) Describe and analyse the relative importance of the work of: James Watson; FrancisCrick; Rosalind Franklin and Maurice Wilkins in determining the structure of DNA andthe impact of collaboration and communication in scientific research.


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5. Reproductive technologies.

Current reproductive techniques


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Current reproductive techniques

Artificial insemination is the injection of selected male sperm into a selectedfemale of the same species. It reduces variation and prevents naturalselection. It is normally carried out by animal breeders to instill certain wantedtraits into the offspring e.g. in race horses the ability to sprint or stay in races.

Artificial pollination is the transfer of pollen from one selected flower toanother. It again defeats natural selection and variation. It is carried out byagriculturists to promote certain traits in the fruit, grain, flower or vegetable

being grown e.g. Mendel's work.Cloning is the development of new individual organisms from body cells,hence they are genetically identical to the parent cells. All bacteria and singlecelled organisms, some insects or plants reproduce asexually and henceproduce clones of themselves. Cloning again produces no variation andreduces biological diversity in the species. The worlds first cloned animal wasDolly the sheep, created in 1996 in Scotland.

In all three cases genetic variability within the species will be been reduced.

CloningThere are two main types of cloning: cellular cloning andorganism cloning.


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CloningCellular cloning is to derive a population of cells from asingle cell. In the case of unicellular organisms such asbacteria and yeast, this process is simple, however, in thecase of cell cultures from multi-cellular organisms, cellcloning is an arduous task as these cells will not readilygrow in standard media

Somatic cell nuclear transfer can be used to create aclonal embryo. The most likely purpose for this is toproduce embryos for use in research, particularly stemcell research.

Organism cloning refers to the procedure of creating a

new multicellular organism, genetically identical toanother. This process entails the transfer of a nucleusfrom a donor adult cell (somatic cell) to an egg fromwhich the original nucleus has been removed. If the eggbegins to divide normally it is transferred into the uterusof the surrogate mother.

Dolly was cloned by this method at the Roslin Institute in

Scotland and lived there until her death (aged 6), she wasborn after 277 eggs were used to create 29 embryos,which only produced three lambs at birth, only one ofwhich lived. Some other species that have been clonedsuccessfully are: Mice(1986); Rhesus Monkey(2000);Mule (2003) and Horse (2003)

Transgenic species


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Transgenic species

Transgenic animals are made when a gene or genes are transferred from

a donor species to a host species (the inserted genes are called trans-genes). The foreign genes must be inserted into sex cells, so that everycell of the offspring will contain the same modified genetic material,which will be inherited by future generations. There are three basicmethods of producing transgenic animals:

Embryonic stem cell-mediated gene transfer:

DNA Micro-injection:Retrovirus-Mediated Gene Transfer

Gene transfer by micro-injection is the predominant method used toproduce transgenic farm animals. Since the insertion of DNA results in arandom process, transgenic animals are mated to ensure that theiroffspring acquire the desired trans-gene.

Some transgenic animals are produced for specific economic traits. e.g.transgenic cattle were created to produce milk containing particularhuman proteins for the treatment of human emphysema.

Other animals are made to exhibit disease symptoms so that effectivetreatment can be studied, e.g. transgenic mice were produced that wouldcatch polio, to study possible cures for human use (polio cannot infectnormal mice)

Ethics of transgenesis


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Ethics of transgenesis

Genetically modified bacteria are used to produce the protein insulin to treat diabetes.Similar bacteria have been used to produce clotting factors to treat haemophilia.

Transgenesis in Salmon has resulted in dramatic growth enhancement . These fish havebeen created for use in the aquaculture industry to increase meat production and,potentially, reduce fishing pressure on wild stocks.

Transgenic plants have been engineered to possess several desirable traits, includingresistance to pests, herbicides or harsh environmental conditions and increasednutritional value

Some of the ethical questions that need to be debated might be:

Is human welfare the only consideration? What about the welfare of other organisms?

Should the focus be on in vitro transgenic cells rather than on live animals ?

Will transgenic animals change the direction of evolution, which may result in drasticconsequences for nature and humans alike?

Could transgenic organisms give rise to new diseases for which we have no cure?

Could transgenic animals contaminate wild stocks and cause ecological disasters?

Should transgenic animals be produced for profit or for entertainment (e.g. fluorescentgold fish or rabbits)?

Should there be an internationally agreed protocol for the production of transgenicspecies?

Impact


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pIn 1900, the global population was approximately 1.6 billion. It will explode to 10 billion

by 2030.Using biotechnology to increase the productivity of our animals is a variation on theage-old practice of selective breeding. Genetic modification of animals by humans hasalready created all of our domesticated livestock and companion animals

Now genetic engineers are taking the next step and developing transgenic animals toprovide solutions for disease treatment, organ transplant shortage and food production.

Increased public demand for seafood and dwindling natural marine habitats have

encouraged the study of ways that biotechnology can increase the production of marinefood products

The benefits of transgenic fish like salmon include increased growth rates and improveddisease resistance.

Transgenic salmon grow faster than other salmon but the offspring of these fish have ahigh and early mortality rate: genetically engineered fish are three times more likely todie prematurely than wild fish.

The growth gene that gives these super fish reproductive advantage could spreadsthrough the native population quickly, genetic diversity would be minimized andbecause of the high mortality native fish populations could dwindle and eventuallybecome extinct.

To reduce the chance of contaminating wild stocks with transgenic genes, only sterile allfemale transgenic salmon should be farmed. But what controls could be enforced locallyand world wide?

Revision questions - 5


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q

1) Identify how the following current reproductive techniques may alter thegenetic composition of a population: artificial insemination; artificialpollination; cloning

2) Describe a methodology used in cloning

3) Outline the processes used to produce transgenic species and includeexamples of this process and reasons for its use

4) Identify examples of the use of transgenic species and discuss the ethicalissues arising from the development and use of transgenic species

5) Discuss the potential impact of the use of reproduction technologies on thegenetic diversity of species using a named plant and animal example that havebeen genetically altered

HSC Biology Blue Print of Life

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