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Mendel and Mendel and HeredityHeredity

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Gregor Gregor MendelMendel

(1822-1884)(1822-1884)

Responsible Responsible for the for the Laws Laws

governing governing Inheritance Inheritance of Traitsof Traits

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Gregor Johann MendelGregor Johann MendelAustrian monkAustrian monkStudied the Studied the inheritanceinheritance of of traits in traits in pea pea plantsplantsDeveloped the Developed the laws of laws of inheritanceinheritanceMendel's work Mendel's work was not recognized was not recognized until the turn of until the turn of thethe 20th century 20th century

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Gregor Johann MendelGregor Johann MendelBetween Between 1856 and 1856 and 1863,1863, Mendel Mendel cultivated and cultivated and tested some tested some 28,000 28,000 pea plantspea plantsHe found that He found that the plants' the plants' offspring retained offspring retained traits of the traits of the parentsparentsCalled theCalled the “Father of “Father of Genetics"Genetics"

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Mendel stated Mendel stated that physical that physical traits are traits are inherited as inherited as “particles”“particles”Mendel did not Mendel did not know that the know that the “particles” were “particles” were actually actually Chromosomes & DNAChromosomes & DNA

Mendel & Particulate Mendel & Particulate InheritanceInheritance

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Genetic TerminologyGenetic Terminology

GeneticsGenetics - study of - study of heredityheredityHeredityHeredity - passing of - passing of traits from parent to traits from parent to offspring offspring TraitTrait - any characteristic - any characteristic that can be passed from that can be passed from parent to offspringparent to offspring

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Types of Genetic CrossesMonohybrid cross

- cross involving a single traitex. flower color Dihybrid cross - cross involving two traits ex. flower color & plant height

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Punnett SquarePunnett Square

Used to help Used to help solve solve genetics genetics problemsproblems

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Designer Designer “Genes”“Genes”

AllelesAlleles - - two forms of a two forms of a gene gene (dominant & recessive)(dominant & recessive) DominantDominant - - stronger of two genes stronger of two genes expressed in the hybrid; expressed in the hybrid; represented byrepresented by aa capital letter capital letter (R)(R) RecessiveRecessive - - gene that shows up gene that shows up less often in a cross; represented less often in a cross; represented by aby a lowercase letter (r)lowercase letter (r)

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Genes and Physical Genes and Physical TraitsTraits

GenotypeGenotype - - gene gene combination for a traitcombination for a trait (e.g. RR, Rr, rr) (e.g. RR, Rr, rr) PhenotypePhenotype - - the physical the physical feature resulting from a feature resulting from a genotypegenotype (e.g. red, white)(e.g. red, white)

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Genotype & Phenotype in Genotype & Phenotype in FlowersFlowers

Genotype of alleles:Genotype of alleles:RR = red flower= red flowerrr = yellow flower= yellow flower

All genes occur in pairs, so All genes occur in pairs, so 22 allelesalleles affect a affect a characteristiccharacteristic

Possible combinations are:Possible combinations are:GenotypesGenotypes RRRR RRrr rrrr

PhenotypesPhenotypes RED RED RED RED YELLOWYELLOW

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GenotypesGenotypesHomozygousHomozygous genotype - gene genotype - gene combination involving 2 combination involving 2 dominant or 2 recessive genes dominant or 2 recessive genes (ex RR or rr);(ex RR or rr); also called also called pure pure  HeterozygousHeterozygous genotype - gene genotype - gene combination of one dominant & combination of one dominant & one recessive allele (one recessive allele (ex Rr);ex Rr); also calledalso called hybridhybrid

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Genes Genes andand Environment Environment Determine CharacteristicsDetermine Characteristics

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Mendel’s Pea Mendel’s Pea Plant Plant

ExperimentsExperiments

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Reproduction in Flowering Reproduction in Flowering PlantsPlants

Pollen contains spermPollen contains sperm

Produced by the Produced by the stamenstamen

Ovary contains eggsOvary contains eggs

Found inside the Found inside the flowerflower

Pollen carries sperm to Pollen carries sperm to the eggs for the eggs for fertilizationfertilization

Self-fertilizationSelf-fertilization can occur in the can occur in the same flowersame flower

Cross-fertilizationCross-fertilization can occur between can occur between flowersflowers

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Mendel’s Mendel’s Experimental MethodsExperimental Methods

Mendel Mendel hand-hand-pollinatedpollinated flowers flowers using a using a paintbrushpaintbrushHe could He could snip the snip the stamensstamens to to prevent self-prevent self-pollinationpollination

He traced traits He traced traits through the through the several several generationsgenerations

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How Mendel BeganHow Mendel Began

Mendel Mendel produced produced purepure strains by strains by allowing allowing the plants the plants to to self-self-pollinatepollinate for for several several generationgenerationss

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Seven Pea Plant TraitsSeven Pea Plant Traits

Seed shapeSeed shape --- Round --- Round (R)(R) or Wrinkled or Wrinkled (r)(r)Seed ColorSeed Color ---- Yellow ---- Yellow (Y)(Y) or  Green or  Green (y)(y)Pod ShapePod Shape --- Smooth --- Smooth (S)(S) or wrinkled or wrinkled (s)(s)Pod ColorPod Color ---  Green ---  Green (G)(G) or Yellow or Yellow (g)(g)Flower positionFlower position---Axial ---Axial (A)(A) or Terminal or Terminal (a)(a)Plant HeightPlant Height --- Tall --- Tall (T)(T) or Short or Short (t)(t)Flower color Flower color --- --- Purple Purple (P)(P) or white or white (p)(p)

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Mendel’s Experimental Mendel’s Experimental ResultsResults

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What Do the Peas Look What Do the Peas Look Like?Like?

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GenerationsGenerationsParental PParental P11 Generation Generation = the parental = the parental generation in a breeding experimentgeneration in a breeding experiment..

FF11 generation generation = the first-generation = the first-generation offspring in a breeding experiment. offspring in a breeding experiment. (1st (1st filial generation)filial generation)

From breeding individuals from the PFrom breeding individuals from the P11 generationgeneration

FF22 generation generation = the second-generation = the second-generation offspring in a breeding experiment. offspring in a breeding experiment. (2nd filial generation)(2nd filial generation)

From breeding individuals from the FFrom breeding individuals from the F11 generationgeneration

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Following the Following the GenerationsGenerations

Cross 2 Cross 2 Pure Pure

PlantsPlantsTT x ttTT x tt

Results Results in all in all HybridsHybrids

TtTt

Cross 2 Cross 2 HybridsHybrids

getget3 Tall & 1 3 Tall & 1

ShortShortTT, Tt, ttTT, Tt, tt

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Monohybrid Monohybrid CrossesCrosses

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Trait: Seed ShapeTrait: Seed Shape

Alleles: Alleles: RR – Round – Round rr – Wrinkled – Wrinkled

Cross: Cross: RoundRound seedsseeds xx Wrinkled Wrinkled seedsseeds

RRRR xx rr rr

PP11 Monohybrid Cross Monohybrid Cross

R

R

rr

Rr

RrRr

Rr

Genotype(s):Genotype(s): RrRr

Phenotype(s)Phenotype(s): RoundRound

GenotypicGenotypicRatio:Ratio: All All alike Rralike Rr

PhenotypicPhenotypicRatio:Ratio: All All alike Rralike Rr

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PP11 Monohybrid Cross Review Monohybrid Cross Review

Homozygous dominant x Homozygous dominant x Homozygous recessiveHomozygous recessiveOffspringOffspring allall HeterozygousHeterozygous (hybrids)(hybrids)Offspring calledOffspring called FF11 generationgenerationGenotypic & Phenotypic ratio Genotypic & Phenotypic ratio isis ALL ALIKEALL ALIKE

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Trait: Seed ShapeTrait: Seed Shape

Alleles: Alleles: RR – Round – Round rr – Wrinkled – Wrinkled

Cross: Cross: RoundRound seeds seeds xx Round Round seedsseeds

RrRr xx Rr Rr

FF11 Monohybrid Cross Monohybrid Cross

R

r

rR

RR

rrRr

Rr

Genotype:Genotype: RR, Rr, RR, Rr, rrrr

PhenotypePhenotype: Round &Round & wrinkledwrinkled

G.Ratio:G.Ratio:1 RR:2 Rr:1 1 RR:2 Rr:1 rrrr

P.Ratio:P.Ratio: 3:1 3:1

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FF11 Monohybrid Cross Review Monohybrid Cross Review

Heterozygous x heterozygousHeterozygous x heterozygousOffspring:Offspring:25% Homozygous dominant25% Homozygous dominant RRRR50% Heterozygous50% Heterozygous RrRr25% Homozygous Recessive25% Homozygous Recessive rrrrOffspring calledOffspring called FF22 generationgenerationGenotypic ratio isGenotypic ratio is 1:2:11:2:1Phenotypic RatioPhenotypic Ratio is 3:1 is 3:1

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……And Now the Test CrossAnd Now the Test Cross

Mendel then crossed a Mendel then crossed a purepure & a & a hybridhybrid from his from his FF2 2 generationgeneration

This is known as an This is known as an FF22 or test or test

crosscross

There are There are twotwo possible possible testcrosses:testcrosses:Homozygous dominant x HybridHomozygous dominant x HybridHomozygous recessive x HybridHomozygous recessive x Hybrid

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Trait: Seed ShapeTrait: Seed Shape

Alleles: Alleles: RR – Round – Round rr – Wrinkled – Wrinkled

Cross: Cross: RoundRound seedsseeds xx Round Round seedsseeds

RRRR xx Rr Rr

FF22 Monohybrid Cross (1 Monohybrid Cross (1stst))

R

R

rR

RR

RrRR

Rr

Genotype:Genotype: RR, RR, RrRr

PhenotypePhenotype: RoundRound

GenotypicGenotypicRatio:Ratio: 1:11:1

PhenotypicPhenotypicRatio:Ratio: All All alikealike

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Trait: Seed ShapeTrait: Seed Shape

Alleles: Alleles: RR – Round – Round rr – Wrinkled – Wrinkled

Cross: Cross: WrinkledWrinkled seedsseeds xx Round Round seedsseeds

rrrr xx Rr Rr

FF22 Monohybrid Cross (2nd) Monohybrid Cross (2nd)

r

r

rR

Rr

rrRr

rr

Genotype:Genotype: Rr, Rr, rrrr

PhenotypePhenotype: Round & Round & WrinkledWrinkled

G. Ratio:G. Ratio: 1:11:1

P.Ratio:P.Ratio: 1:1 1:1

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FF22 Monohybrid Cross Review Monohybrid Cross Review

Homozygous x Homozygous x heterozygous(hybrid)heterozygous(hybrid)Offspring:Offspring:50% Homozygous 50% Homozygous RR or rrRR or rr50% Heterozygous50% Heterozygous RrRrPhenotypic RatioPhenotypic Ratio is 1:1 is 1:1Called Called Test CrossTest Cross because because the offspring have the offspring have SAMESAME genotype as parentsgenotype as parents

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Mendel’s LawsMendel’s Laws

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Law of DominanceLaw of Dominance

In a cross of parents that In a cross of parents that are are pure for contrasting pure for contrasting traitstraits, only one form of the , only one form of the trait will appear in the trait will appear in the next generation.next generation.

All the offspring will be All the offspring will be heterozygous and express heterozygous and express only the only the dominant trait.dominant trait.

RR x rr RR x rr yieldsyields all Rr (round all Rr (round seeds)seeds)

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Law of DominanceLaw of Dominance

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Law of SegregationLaw of Segregation

During the During the formation of gametesformation of gametes (eggs or sperm), the (eggs or sperm), the two two allelesalleles responsible for a trait responsible for a trait separateseparate from each other. from each other.

Alleles for a trait are then Alleles for a trait are then "recombined" at fertilization"recombined" at fertilization, , producing the genotype for the producing the genotype for the traits of the offspringtraits of the offspring.

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Applying the Law of Applying the Law of SegregationSegregation

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Law of Independent Law of Independent AssortmentAssortment

Alleles for Alleles for differentdifferent traits traits are distributed to sex cells are distributed to sex cells (& offspring) independently (& offspring) independently of one another.of one another.

This law can be illustrated This law can be illustrated using using dihybrid crossesdihybrid crosses..

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Dihybrid CrossDihybrid CrossA breeding experiment that tracks A breeding experiment that tracks the the inheritance of two traitsinheritance of two traits..

Mendel’s Mendel’s “Law of Independent “Law of Independent Assortment”Assortment”

a. Each pair of alleles segregates a. Each pair of alleles segregates independentlyindependently during gamete formation during gamete formation

b. Formula: 2b. Formula: 2nn (n = # of heterozygotes) (n = # of heterozygotes)

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Question:Question:How many gametes will be How many gametes will be

produced for the following produced for the following allele arrangements?allele arrangements?

22nn (n = # of heterozygotes) (n = # of heterozygotes)

1.1. RrYyRrYy

2.2. AaBbCCDdAaBbCCDd

3.3. MmNnOoPPQQRrssTtQqMmNnOoPPQQRrssTtQq

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Answer:Answer:1. RrYy: 21. RrYy: 2nn = 2 = 222 = 4 gametes = 4 gametes

RY Ry rY ryRY Ry rY ry

2. AaBbCCDd: 22. AaBbCCDd: 2nn = 2 = 233 = 8 gametes = 8 gametes

ABCD ABCd AbCD AbCdABCD ABCd AbCD AbCd

aBCD aBCd abCD abCDaBCD aBCd abCD abCD

3. MmNnOoPPQQRrssTtQq: 23. MmNnOoPPQQRrssTtQq: 2nn = 2 = 266 = = 64 gametes64 gametes

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Dihybrid CrossDihybrid CrossTraits: Seed shape & Seed colorTraits: Seed shape & Seed colorAlleles:Alleles: R round r wrinkled Y yellow y green

RrYy x RrYy

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

All possible gamete combinationsAll possible gamete combinations

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Dihybrid CrossDihybrid Cross

RRYY

RRYy

RrYY

RrYy

RRYy

RRyy

RrYy

Rryy

RrYY

RrYy

rrYY

rrYy

RrYy

Rryy

rrYy

rryy

Round/Yellow: 9

Round/green: 3

wrinkled/Yellow: 3

wrinkled/green: 1

9:3:3:1 phenotypic ratio

RYRY RyRy rYrY ryry

RYRY

RyRy

rYrY

ryry

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Dihybrid CrossDihybrid Cross

Round/Yellow: 9Round/green: 3wrinkled/Yellow: 3wrinkled/green: 1

9:3:3:1

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Summary of Mendel’s lawsSummary of Mendel’s laws

LAWLAW PARENT CROSSPARENT CROSS OFFSPRINGOFFSPRING

DOMINANCEDOMINANCE TT x ttTT x tt tall x shorttall x short

100% Tt 100% Tt talltall

SEGREGATIONSEGREGATION Tt x TtTt x Tt tall x talltall x tall

75% tall 75% tall 25% short25% short

INDEPENDENT INDEPENDENT ASSORTMENTASSORTMENT

RrGg x RrGgRrGg x RrGg round & round & green x green x round & round & greengreen

9/16 round seeds & green 9/16 round seeds & green pods pods

3/16 round seeds & yellow 3/16 round seeds & yellow pods pods

3/16 wrinkled seeds & 3/16 wrinkled seeds & green pods green pods

1/16 wrinkled seeds & 1/16 wrinkled seeds & yellow podsyellow pods

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Incomplete DominanceIncomplete Dominanceandand

CodominanceCodominance

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Incomplete DominanceIncomplete Dominance

F1 hybrids F1 hybrids have an appearance somewhat in betweenin between the phenotypes phenotypes of the two parental varieties.

Example:Example: snapdragons (flower)snapdragons (flower)red (RR) x white (rr)

RR = red flowerRR = red flowerrr = white flower

All Rr =All Rr = pink pink(heterozygous pink)(heterozygous pink)

R

R

r r

RrRr RrRr

RrRrRrRr

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Incomplete DominanceIncomplete Dominance

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CodominanceCodominanceTwo allelesTwo alleles are expressed ( are expressed (multiple multiple allelesalleles) in ) in heterozygous heterozygous individualsindividuals..

Example:Example: blood type blood type

1.1. type Atype A = I= IAAIIAA or I or IAAii2.2. type Btype B = I= IBBIIBB or I or IBBii3.3. type ABtype AB = I= IAAIIBB

4.4. type Otype O = ii= ii

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Codominance ProblemCodominance ProblemExample: homozygous male Type B (IBIB)

x heterozygous female Type A (IAi)

IAIB IBi

IAIB IBi

1/2 = IAIB

1/2 = IBi

IB

IA i

IB

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Another Codominance Another Codominance ProblemProblem

• Example:Example: male Type O (ii) x female type AB (IAIB)

IAi IBi

IAi IBi

1/2 = IAi1/2 = IBi

i

IA IB

i

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Sex-linked TraitsSex-linked Traits

Traits (genes) located on Traits (genes) located on the sex chromosomesthe sex chromosomes

Sex chromosomes are Sex chromosomes are X and YX and YXXXX genotype for females genotype for femalesXYXY genotype for males genotype for malesMany Many sex-linked traitssex-linked traits carried on carried on XX chromosome chromosome

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Sex-linked TraitsSex-linked Traits

Sex ChromosomesSex Chromosomes

XX chromosome - female Xy chromosome - male

fruit flyeye color

Example: Example: Eye color in Eye color in fruit fliesfruit flies

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Sex-linked Trait Sex-linked Trait ProblemProblem

Example: Eye color in fruit flies (red-eyed male) x (white-eyed female) XRY x XrXr

Remember: the Y chromosome in males does not carry traits.

RR = red eyedRr = red eyedrr = white eyedXY = maleXX = female

XR

Xr Xr

Y

XR Xr

Xr Y

XR Xr

Xr Y50% red eyed female50% white eyed male

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PedigreePedigree

PedigreePedigree - a family history - a family history that shows how a trait is that shows how a trait is inherited over several inherited over several generationsgenerations

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Pedigree - Female Pedigree - Female CarriersCarriers

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