1 Mendelelian Genetics copyright cmassengale. 2 Gregor Johann Mendel Studied the inheritance of traits in pea plants Developed the laws of inheritance

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Mendelelian Mendelelian GeneticsGenetics

copyright cmassengale

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Gregor Johann MendelGregor Johann MendelStudied the Studied the inheritanceinheritance of of traits in traits in pea plantspea plants

Developed the Developed the laws of inheritancelaws of inheritance

Mendel's work Mendel's work was not was not recognized until recognized until the turn of thethe turn of the 20th century20th century


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Gregor Johann MendelGregor Johann Mendel

He found that He found that the plants' the plants' offspring offspring retained retained traits of traits of the parentsthe parents

Called theCalled the “Father of “Father of Genetics"Genetics"


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Genetic TerminologyGenetic Terminology

GeneGene – a segment of DNA that is – a segment of DNA that is located in a chromosome & located in a chromosome & codes for a specific heredity traitcodes for a specific heredity traitTraitTrait - any characteristic that - any characteristic that can be passed from parent to can be passed from parent to offspring offspring HeredityHeredity - passing of traits from - passing of traits from parent to offspring parent to offspring GeneticsGenetics - study of heredity - study of heredity


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Types of Genetic Types of Genetic CrossesCrosses

Cross Cross – mating of two individuals– mating of two individualsGameteGamete – male and female sex cells (egg & – male and female sex cells (egg & sperm)sperm)FertilizationFertilization – the union of male and – the union of male and female gametes to form a zygote.female gametes to form a zygote.Monohybrid cross Monohybrid cross - - cross involving a single cross involving a single trait e.g. flower color trait e.g. flower color Dihybrid crossDihybrid cross - - cross involving two traits cross involving two traits e.g. flower color & plant heighte.g. flower color & plant height


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Punnett SquarePunnett Square

Used to help Used to help solve solve genetics genetics problemsproblems


7copyright cmassengale

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Designer Designer “Genes”“Genes”

AllelesAlleles - - two forms of a two forms of a gene gene

Ex. on chromosomes that code for ht. Ex. on chromosomes that code for ht. there would be 2 alleles, short & tall)there would be 2 alleles, short & tall) DominantDominant - - visible, observable trait; visible, observable trait; stronger of two genes expressed in the stronger of two genes expressed in the hybrid and masks the recessive. hybrid and masks the recessive. represented byrepresented by aa capital letter (R)capital letter (R) RecessiveRecessive – – hidden trait; gene that hidden trait; gene that shows up less often in a cross; shows up less often in a cross; represented by arepresented by a lowercase letter (r)lowercase letter (r)


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More TerminologyMore TerminologyGenotypeGenotype - - gene combination gene combination

for a trait; genetic make up of an for a trait; genetic make up of an organismorganism (e.g. RR, Rr, rr) (e.g. RR, Rr, rr)

PhenotypePhenotype - - the physical the physical feature or visible traits of an feature or visible traits of an organismorganism

(e.g. red, white) (e.g. red, white)


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GenotypesGenotypesHomozygousHomozygous genotype – both genotype – both

alleles are identical for a specific alleles are identical for a specific trait; 2 dominant or 2 recessive trait; 2 dominant or 2 recessive genes; genes;

(e.g. RR or rr);(e.g. RR or rr); also called also called pure pure HeterozygousHeterozygous genotype – having genotype – having 2 different alleles for a given 1 2 different alleles for a given 1 dominant & 1 recessive allele dominant & 1 recessive allele

((e.g. Rr);e.g. Rr); also called also called hybridhybrid


Mendel’s Pea Plant ExperimentsMendel’s Pea Plant Experiments

copyright cmassengale 11

Mendel crossed 2 plants with different characters, or forms, for the same trait.

Ex. 1 tall & 1 short*The plants that grew were hybrid.

Hybrid – are the offspring of crosses between parents with different traits.

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Why peas,Why peas, Pisum Pisum sativumsativum??Can be grown in a Can be grown in a

small areasmall area Produce Produce lots of lots of offspring offspring Produce Produce purepure plants when allowed plants when allowed to to self-pollinateself-pollinate several generations several generations Can be Can be artificially artificially cross-pollinatedcross-pollinated


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How Mendel BeganHow Mendel BeganMendel Mendel produced produced purepure strains by strains by allowing allowing the plants the plants to to self-self-pollinatepollinate for for several several generatiogenerationsns copyright cmassengale

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Eight Pea Plant TraitsEight 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 ((yy))

Pod ShapePod Shape --- Smooth --- Smooth (S)(S) or wrinkled or wrinkled ((ss))Pod ColorPod Color --- Green --- Green (G)(G) or Yellow or Yellow (g)(g)Seed Coat ColorSeed Coat Color ---Gray ---Gray (G)(G) or White or White (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 ((pp))


Experiment I Concluded:*Each trait is based on two genes, one from the

mother and the other from the father *The hybrid plants looked like only 1 parent

and the character of the other parent seemed to disappear.

*Each trait is controlled by 1 gene.

Alleles- controls the different forms of a gene.Genes- chemical factors that determine traits.Phenotype is based on Genotype


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Law of DominanceLaw of Dominance *States that some alleles are dominant & others are recessive.

*Whenever a living thing inherits a dominant allele, that trait is visible.

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

RR x rr yields all Rr (round 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 formation of gametesgametes (eggs or sperm), the (eggs or sperm), the two allelestwo alleles responsible for a responsible for a trait 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 producing the genotype for the traits of the offspringthe traits of the offspring.


Experiment II: Law of Segregation

Mendel crossed a tall plant (dominant) with a short plant (recessive), the F1 plant inherited an allele for tallness from the tall parent & an allele for shortness from the short parent. Pg. 265

Mendel allowed his hybrid plants to self-pollinate.

Some showed recessive traits, the recessive traits did not disappear.

Earlier, the dominant masked the recessive, so it was not visible.

Alleles for the same trait can be separated.copyright cmassengale 19

Law of Segregation

Segregation – When sex cells, or gametes, are formed. Each gamete carries only 1 copy of each gene.

Therefore, each F1 plant produces 2 types of gametes (some with an allele for tallness & some with an allele for shortness). Ex. T, t, T, t = TT, Tt, Tt, tt


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Applying the Law of Applying the Law of SegregationSegregation



Probability – the likelihood that a particular event will occur. Ex. Flipping a coin. The

probability that it will land on tails is ½.

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Law of Independent Law of Independent AssortmentAssortment

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

This helps account for genetic This helps account for genetic variations.variations.

This law can be illustrated using This law can be illustrated using dihybrid crossesdihybrid crosses. Ex Pea shape & . Ex Pea shape & pea colorpea color


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Generation “Gap”Generation “Gap”Parental 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

HybridsHybridsTtTt

Cross 2 Cross 2 HybridsHybrids

getget3 Tall & 1 3 Tall & 1

ShortShortTT, Tt, ttTT, Tt, tt


A Punnett Square shows:


*All the possible results of a genetic cross.

*The genotypes of the offspring.

*The alleles in the gametes of each parent.

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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:Genotype: RrRr

PhenotypePhenotype: RoundRound

GenotypicGenotypicRatio:Ratio: All alikeAll alike

PhenotypicPhenotypicRatio:Ratio: All alike All alikecopyright cmassengale

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PP11 Monohybrid Cross Monohybrid Cross ReviewReviewHomozygous dominant x Homozygous dominant x

Homozygous recessiveHomozygous recessiveOffspringOffspring allall HeterozygousHeterozygous (hybrids)(hybrids)Offspring calledOffspring called FF11 generation generation

Genotypic & Phenotypic ratio Genotypic & Phenotypic ratio isis ALL ALIKEALL ALIKE


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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 && wrinkled wrinkled

G.Ratio:G.Ratio: 1:2:11:2:1

P.Ratio:P.Ratio: 3:1 3:1copyright cmassengale

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FF11 Monohybrid Cross Monohybrid Cross ReviewReviewHeterozygous x heterozygousHeterozygous x heterozygousOffspring:Offspring:

25% Homozygous dominant25% Homozygous dominant RRRR50% Heterozygous50% Heterozygous RrRr25% Homozygous Recessive25% Homozygous Recessive rrrrOffspring calledOffspring called FF22 generation generationGenotypic 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 And Now the Test CrossCross

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 cross or test cross

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


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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 alike All alike


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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, rrRr, rr

PhenotypePhenotype: Round & Round & WrinkledWrinkled

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

P.Ratio:P.Ratio: 1:1 1:1copyright cmassengale

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FF22 Monohybrid Cross Monohybrid Cross ReviewReviewHomozygous 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 the because the offspring have offspring have SAMESAME genotype genotype as parentsas parents


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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 during gamete formationformation

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 allele produced for the following allele arrangements?arrangements?

Remember:Remember: 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


Experiment III

*Mendel wanted to see if genes that determine 1 trait have anything to do with genes that determine another.

*He followed 2 different genes as they passed from one generation to the next.

*Mendel crossed true-breeding plants - round yellow peas (RRYY) with wrinkled green peas (rryy).

*The F1 offspring were all round & yellow showing that both were dominant alleles. The genotype is RrYy. Pg. 270


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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 combinationscopyright cmassengale

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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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Test CrossTest CrossA mating between an individual of A mating between an individual of unknown unknown

genotype genotype and a and a homozygous recessivehomozygous recessive individual.individual.

Example:Example: bbC__ bbC__ x x bbccbbcc

BB = brown eyesBB = brown eyesBb = brown eyesBb = brown eyesbb = blue eyesbb = blue eyes

CC = curly hairCC = curly hairCc = curly hairCc = curly haircc = straight haircc = straight hair

bCbC b___b___

bcbc


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Test CrossTest Cross

Possible results:Possible results:

bCbC b___b___

bcbc bbCc bbCc

C bCbC b___b___

bcbc bbCc bbccor

c


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Summary of Mendel’s Summary of Mendel’s lawslaws

LAWLAW PARENT PARENT CROSSCROSS 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


Pedigrees*Pedigrees – are graphic representations

of a family tree, which allows for patterns of inheritance to be seen.

*Each horizontal row of circles and squares represents a generation.

*People that do not show the trait but are heterozygous (Tt) for the trait are called carriers.


Pedigree on mouse color


Different Patterns of Dominant & Recessive


Incomplete Dominance – 1 allele is not completely dominant over another. Ex. Red flower

(RR) & white flower (WW), F1 is a pink flower (RW). Pg. 272

Codominance – both alleles contribute to the phenotype.

Ex. A cross of a black chicken (BB) with a white chicken (WW) will produce all speckled offspring

(BBWW); colors appear separately.

Different Patterns of Dominant & Recessive

Multiple Alleles – have more than 2 alleles. Ex. Coat color in rabbits.

Polygenic Traits – traits controlled by 2 or more genes; “having many genes”. Ex. Variation in human skin color.


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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

R

R

r r


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RrRr

RrRr

RrRr

RrRr

RR

RR

rr

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

produces theproduces theFF11 generation generation

r


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CodominanceCodominanceTwo allelesTwo alleles are expressed ( are expressed (multiple multiple

allelesalleles) in ) in heterozygous individualsheterozygous individuals..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 the Traits (genes) located on the sex chromosomessex chromosomes

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

on X chromosomeon X 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 fruit Eye color in fruit fliesflies


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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


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Sex-linked Trait Solution:Sex-linked Trait Solution:

XR Xr

Xr Y

XR Xr

Xr Y

50% red eyed female

50% white eyed male

XR

Xr Xr

Y


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Female CarriersFemale Carriers


Documents

1 Mendelelian Genetics copyright cmassengale. 2 Gregor Johann Mendel Studied the inheritance of traits in pea plants Developed the laws of inheritance