Mendel and HeredityMendel and Heredity

Chapter 8Chapter 8

8.1 The Origins of Genetics8.1 The Origins of Genetics Heredity is the passing Heredity is the passing

of characters from of characters from parents to offspringparents to offspring Used throughout history Used throughout history

to alter crops and to alter crops and domestic animalsdomestic animals

Gregor Johann Mendel – Gregor Johann Mendel – Austrian MonkAustrian Monk Used pea plants and bred Used pea plants and bred

different varietiesdifferent varieties Developed rules to Developed rules to

accurately predict accurately predict patterns of hereditypatterns of heredity

Why Peas?Why Peas? 2 characters have clearly different 2 characters have clearly different

formsforms Character = inherited characteristic Character = inherited characteristic

(color)(color) Trait = single form of character Trait = single form of character

(purple)(purple)

Male and female reproductive Male and female reproductive parts are in same flowerparts are in same flower Can control fertilizationCan control fertilization Flower can fertilize itself (self-Flower can fertilize itself (self-

fertilization) or can cross pollen from fertilization) or can cross pollen from 1 plant to another (cross-pollination)1 plant to another (cross-pollination)

Peas are small, grow easily, Peas are small, grow easily, mature quickly, and produces mature quickly, and produces many seeds so results obtained many seeds so results obtained quicklyquickly

Traits Expressed as Simple RatiosTraits Expressed as Simple Ratios Mendel started by looking at 1 characteristic Mendel started by looking at 1 characteristic

(monohybrid), such as color, with 1 pair of (monohybrid), such as color, with 1 pair of contrasting traits, purple or white flowerscontrasting traits, purple or white flowers

Only allowed plants to self-pollinate for many Only allowed plants to self-pollinate for many generations generations True-breeding – all offspring show only 1 traitTrue-breeding – all offspring show only 1 trait Parental (P) generationParental (P) generation

Cross pollinated 2 P generation plants with Cross pollinated 2 P generation plants with contrasting traitscontrasting traits Offspring called filial (FOffspring called filial (F11) generation) generation Counted numbers of each traitCounted numbers of each trait

Allowed FAllowed F11 generation to self pollinate generation to self pollinate Offspring called FOffspring called F22 generation generation Each characterized and countedEach characterized and counted

Mendel’s ResultsMendel’s Results FF11 showed only 1 form of character other had showed only 1 form of character other had

disappeareddisappeared When FWhen F11 self pollinates other trait reappears in some self pollinates other trait reappears in some

of Fof F22

Found ratio of traits to be 3 to 1Found ratio of traits to be 3 to 1 3 white flowers to 1 purple flower3 white flowers to 1 purple flower Same ratio found for any trait he studiedSame ratio found for any trait he studied

8.2 Mendel’s Theory8.2 Mendel’s Theory

We used to think offspring were blend of We used to think offspring were blend of traitstraitsTall x short = mediumTall x short = medium

Mendel’s experiments showed us this is Mendel’s experiments showed us this is not entirely truenot entirely true

Mendel’s HypothesisMendel’s Hypothesis There are 2 copies of a gene, one from each There are 2 copies of a gene, one from each

parent, for each inherited characteristicparent, for each inherited characteristic There are different versions of genes called There are different versions of genes called

“alleles”“alleles” Tall or shortTall or short

When both versions are present one may be When both versions are present one may be dominant (completely expressed) and the other dominant (completely expressed) and the other may be recessive (not expressed when may be recessive (not expressed when dominant is present)dominant is present)

When you form gametes, alleles separate When you form gametes, alleles separate independently so only one allele in each gameteindependently so only one allele in each gamete

Mendel’s Finding in Modern TermsMendel’s Finding in Modern TermsUse letters to show allelesUse letters to show alleles

Capitol = dominant (T, P, Y, etc…)Capitol = dominant (T, P, Y, etc…)Lower case = recessive (t, p, y, etc…)Lower case = recessive (t, p, y, etc…)Homozygous = letters are same Homozygous = letters are same

Homozygous dominant = TT, PPHomozygous dominant = TT, PPHomozygous recessive = tt, ppHomozygous recessive = tt, pp

Heterozygous = letters are different Heterozygous = letters are different Tt, PpTt, PpOnly dominant allele is expressedOnly dominant allele is expressed

Genotype = set of allelesGenotype = set of allelesWhat you actually have What you actually have TT, Tt, or ttTT, Tt, or tt

Phenotype = what is expressedPhenotype = what is expressedHow it looksHow it looksTall, Tall, or ShortTall, Tall, or Short

Mendel’s Laws of HeredityMendel’s Laws of Heredity Law of SegregationLaw of Segregation

2 alleles for a character segregate when gametes are 2 alleles for a character segregate when gametes are formedformed

Behavior of chromosomes during meiosisBehavior of chromosomes during meiosis

Law of Independent AssortmentLaw of Independent Assortment 1 character does not affect another1 character does not affect another Alleles of different genes separate independently of Alleles of different genes separate independently of

on anotheron another Now know this only applies to genes located on Now know this only applies to genes located on

different chromosomes or that are far apart on same different chromosomes or that are far apart on same chromosomechromosome

8.3 Studying Heredity:8.3 Studying Heredity: Punnett Squares Punnett Squares

Breeders want Breeders want certain certain characteristics characteristics when they breed when they breed (cross) animals(cross) animals

Horticulturists Horticulturists produce plants produce plants with specific with specific characteristicscharacteristics

Punnett SquarePunnett Square Used to predict Used to predict

outcomesoutcomesShows all Shows all

possible possible combinations of combinations of gametesgametes

Put 1Put 1stst parents parents genotype on topgenotype on top

Put 2Put 2ndnd parents parents genotype on sidegenotype on side

Do the crossDo the cross

TT

Tt

Tt

tt

• So in Mendel’s F1 generation, a pure Tall plant bred with a pure short plant can only give 1 kind of offspring due to dominance of tall allele

Determining Unknown Genotypes Determining Unknown Genotypes

How do you know if a tall plant is How do you know if a tall plant is homozygous or heterozygous? They both homozygous or heterozygous? They both look talllook tall

Can do a Test CrossCan do a Test Cross If dominant phenotype is shown with unknown If dominant phenotype is shown with unknown

genotype, cross it with homozygous recessivegenotype, cross it with homozygous recessive

Test Cross ResultsTest Cross Results

If unknown is If unknown is homozygous homozygous dominant, all dominant, all offspring of test offspring of test cross will have cross will have dominant traitdominant trait

Test Cross ResultsTest Cross Results

If unknown is If unknown is heterozygous, heterozygous, offspring of test offspring of test cross will have 2 cross will have 2 dominant and 2 dominant and 2 recessive recessive phenotypesphenotypes

Can use probability calculations to predict Can use probability calculations to predict results of genetic crossesresults of genetic crosses

Probability is the likelihood a specific event Probability is the likelihood a specific event will occurwill occur

Probability = # of 1 kind of possible Probability = # of 1 kind of possible outcome divided by total number of outcome divided by total number of possible outcomespossible outcomes

We will express these as fractionsWe will express these as fractionsChance a coin will come up headsChance a coin will come up heads

1 head / 2 sides = ½1 head / 2 sides = ½

DD = ¼DD = ¼ Dd = 2/4 or ½ Dd = 2/4 or ½ dd = ¼dd = ¼

Dihybrid CrossDihybrid Cross

Uses a Punnett Square to determine Uses a Punnett Square to determine outcomes of 2 traits at one timeoutcomes of 2 traits at one time

Example: Surface and ColorExample: Surface and ColorSurface:Surface: RR, Rr, or rrRR, Rr, or rr round or wrinkledround or wrinkledColor:Color: YY, Yy, yyYY, Yy, yy yellow or yellow or

greengreenWhat are the possible combinations?What are the possible combinations?

RY, Ry, rY, ryRY, Ry, rY, ry

So if you have 2 purebred homozygous So if you have 2 purebred homozygous parents RRYY and rryy and you mate parents RRYY and rryy and you mate them, what do you get?them, what do you get?All offspring will be RrYyAll offspring will be RrYy

What if you have F1 breed?What if you have F1 breed?Make a Punnett Square of possible gametes Make a Punnett Square of possible gametes

for each parentfor each parentWhat possible combos can parents offer?What possible combos can parents offer?

Do you remember FOIL?Do you remember FOIL?RY, Ry, rY, ryRY, Ry, rY, ry

You never have to count the results You never have to count the results of a dihybrid cross between of a dihybrid cross between

heterozygotes!heterozygotes!

9 with both dominant traits9 with both dominant traits3 with first dominant and second recessive3 with first dominant and second recessive3 with first recessive and second dominant3 with first recessive and second dominant1 with both recessive traits1 with both recessive traitsSo 9:3:3:1So 9:3:3:1

Inheritance of TraitsInheritance of Traits PedigreePedigree

Family history that shows how a trait is inherited over Family history that shows how a trait is inherited over several generationsseveral generations

Helpful in tracking genetic disordersHelpful in tracking genetic disorders Carrier – have allele for trait but show no symptomsCarrier – have allele for trait but show no symptoms

Things You Can Find From A PedigreeThings You Can Find From A Pedigree Autosomal or Sex-Autosomal or Sex-

Linked?Linked? If autosomal it will be If autosomal it will be

equal in both sexesequal in both sexes If sex linked If sex linked

generally only found generally only found in malesin malesY linkedY linked

Hairy ear rimsHairy ear rims

X linkedX linked Color-blindnessColor-blindness HemophiliaHemophilia

Dominant or recessiveDominant or recessive Autosomal Dominant – Autosomal Dominant –

every individual with every individual with condition will have parent condition will have parent with conditionwith condition

Achondroplasia – type of Achondroplasia – type of dwarfismdwarfism

Huntington’s Disease – Huntington’s Disease – brain degeneratesbrain degenerates

Autosomal Recessive – 1, Autosomal Recessive – 1, 2, or no parents with 2, or no parents with conditioncondition

Cystic fibrosisCystic fibrosis Sickle cell anemiaSickle cell anemia AlbinismAlbinism

Heterozygous or Heterozygous or HomozygousHomozygous Autosomal Autosomal

homozygous dominant homozygous dominant or heterozygous or heterozygous phenotype will show phenotype will show dominant alleledominant allele

Homozygous Homozygous recessive will show recessive will show recessive allelerecessive allele

2 heterozygous of 2 heterozygous of recessive allele don’t recessive allele don’t show condition but can show condition but can have children that dohave children that do

8.4 Complex Patterns of Heredity8.4 Complex Patterns of Heredity

Complex ControlComplex ControlMost of the time characters display much Most of the time characters display much

more complex patterns than simple dominant-more complex patterns than simple dominant-recessive patternsrecessive patterns

Characters can be influenced by Characters can be influenced by severalseveral genesgenes

Polygenic InheritancePolygenic Inheritance

Several genes affect a characterSeveral genes affect a character These genes may be scattered along same These genes may be scattered along same

chromosome or on different chromosomeschromosome or on different chromosomes Determining the effect of any one gene is difficultDetermining the effect of any one gene is difficult Crossing over and independent assortment Crossing over and independent assortment

create many different offspring comboscreate many different offspring combos Eye color, height, weight, hair, intelligence, and Eye color, height, weight, hair, intelligence, and

skin colorskin color Usually gives a range of expressionUsually gives a range of expression

Polygenic InheritancePolygenic Inheritance

Intermediate CharactersIntermediate Characters Incomplete dominanceIncomplete dominance

Phenotype that is intermediate between 2 parents, Phenotype that is intermediate between 2 parents, neither is completely dominantneither is completely dominant

White x red = pinkWhite x red = pink Straight hair x curly hair = wavy hairStraight hair x curly hair = wavy hair

Multiple AllelesMultiple AllelesCharacters controlled by genes with 3+ Characters controlled by genes with 3+

allelesallelesHumans have ABO blood typesHumans have ABO blood types IIAA, I, IBB, i, iLetters A and B refer to carbohydrates on Letters A and B refer to carbohydrates on

surface of red blood cellssurface of red blood cells i has neither carbohydratei has neither carbohydrate IIAA and I and IBB are dominant over I, but not over are dominant over I, but not over

each other (codominant)each other (codominant)Still only 2 possibilities in a personStill only 2 possibilities in a person

Blood TypesBlood Types

2 forms are displayed 2 forms are displayed at the same timeat the same time

Codominance – both Codominance – both expressed, not expressed, not blendedblended

IIAAIIB B both expressedboth expressed ii = Type Oii = Type O

Characters Influenced by EnvironmentCharacters Influenced by Environment Plants may change color Plants may change color

based on pH of soilbased on pH of soil Arctic foxArctic fox

Summer – enzymes produce Summer – enzymes produce pigments for darker furpigments for darker fur

Winter – no enzymes, no Winter – no enzymes, no pigments to darken furpigments to darken fur

Siamese catsSiamese cats Dark fur in cooler partsDark fur in cooler parts

HumansHumans Height related to nutritionHeight related to nutrition Skin color based on sun Skin color based on sun

exposureexposure Twins are genetically identical, Twins are genetically identical,

any difference is due to any difference is due to environmentenvironment

Genetic DisordersGenetic Disorders

Proteins encoded by genes must function Proteins encoded by genes must function precisely for normal development and functionprecisely for normal development and function

Genes may be damaged or copied wrong Genes may be damaged or copied wrong causing faulty proteinscausing faulty proteins

Mutation = changes in genetic materialMutation = changes in genetic material Rare because cells try to correct errorsRare because cells try to correct errors

Harmful effects produced by inherited mutationsHarmful effects produced by inherited mutations Many carried by recessive allelesMany carried by recessive alleles

Sickle Cell AnemiaSickle Cell Anemia Recessive genetic disorderRecessive genetic disorder Mutated allele produces Mutated allele produces

defective form of defective form of hemoglobin causing red hemoglobin causing red blood cells (rbc) to be blood cells (rbc) to be misshapenmisshapen

These rupture easily These rupture easily causing less Ocausing less O22 to be to be carried and may get stuck carried and may get stuck and cut off blood supplyand cut off blood supply

Recessive allele protects Recessive allele protects heterozygous individuals heterozygous individuals from malariafrom malaria Parasites in sickle rbc dieParasites in sickle rbc die Normal rbc still transport Normal rbc still transport

oxygenoxygen

Cystic FibrosisCystic Fibrosis Most common fatal, Most common fatal,

hereditary, recessive hereditary, recessive disorder in Caucasionsdisorder in Caucasions

1 in 25 has at least 1 1 in 25 has at least 1 copy of defective gene copy of defective gene that makes a protein that makes a protein needed to move chloride needed to move chloride in and out of cellsin and out of cells

Mucus clogs organsMucus clogs organs 1 in 2,500 homozygous 1 in 2,500 homozygous

for cystic fibrosisfor cystic fibrosis No cureNo cure

HemophiliaHemophilia

Impairs bloods ability to clotImpairs bloods ability to clotSex-linkedSex-linkedDozen+ genes code for clotting proteinsDozen+ genes code for clotting proteins1 mutation on X chromosome causes 1 mutation on X chromosome causes

Hemophilia AHemophilia AMales only get 1 X chromosomeMales only get 1 X chromosome

Huntington’s DiseaseHuntington’s Disease

dominant allele on autosomedominant allele on autosome11stst symptoms - mild forgetfulness and symptoms - mild forgetfulness and

irritability in 30’s and 40’sirritability in 30’s and 40’sEventually lose muscle control, spasms, Eventually lose muscle control, spasms,

severe mental illness, and deathsevere mental illness, and death

Treating Genetic DisordersTreating Genetic Disorders

Most can’t be curedMost can’t be curedGenetic Counseling – tells of possible Genetic Counseling – tells of possible

genetic problems with offspring, may be genetic problems with offspring, may be treated if early enoughtreated if early enough

Phenylketonuria (PKU)Phenylketonuria (PKU)

Lack enzyme that converts amino acid Lack enzyme that converts amino acid phenylalanine into tyrosine so it builds up phenylalanine into tyrosine so it builds up in the body and causes severe mental in the body and causes severe mental retardationretardation

Can be placed on phenylalenic dietCan be placed on phenylalenic diet

Gene TherapyGene Therapy

Replace defective genes with normal onesReplace defective genes with normal ones Isolate copy of geneIsolate copy of genePut working copy into a virusPut working copy into a virusVirus infects and puts gene inVirus infects and puts gene in Infected cells are curedInfected cells are cured

Still trying to get this to workStill trying to get this to work