INCOMPLETE DOMINANCEINCOMPLETE DOMINANCEANDAND

CODOMINANCECODOMINANCE

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INCOMPLETE DOMINANCEINCOMPLETE DOMINANCE

Neither allele has “complete” dominance over the other; heterozygous phenotype is a blend of the 2 homozygous phenotypes

Ex: snapdragons R = red W = white RW = pink

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Cross a red (RR) snapdragon with a White (WW) snapdragon. Give the

genotypic and phenotypic ratios.Key: R = red flower WKey: R = red flower W = white

flowerCross: RR x WW

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W W

R

R

Genotypic Ratio:

Phenotypic Ratio:

Answer on next slide…

INCOMPLETE DOMINANCEINCOMPLETE DOMINANCE

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RWRW

RWRW

RWRW

RWRW

RR

RR

WWW

Key: R = red W = whiteCross: RR x WW

Genotypic Ratio:0RR: 4RW: 0WW

Phenotypic Ratio:0 Red: 4 Pink: 0 White

INCOMPLETE DOMINANCEINCOMPLETE DOMINANCE

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Practice: Cross a pink snapdragon with a red snapdragon. Give the expected phenotypic and genotypic ratios.

Key: __________________

Cross: _________________

Genotypic Ratio: ________________________

Phenotypic Ratio: ________________________

INCOMPLETE DOMINANCEINCOMPLETE DOMINANCE

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Practice: Cross a pink snapdragon with a red snapdragon. Give the expected phenotypic and genotypic ratios.

Key: R = red W = white RW = pink

Cross: _RW x RR__

Genotypic Ratio: __2RR: 2RW: 0WW__

Phenotypic Ratio: __2 red: 2 pink: 0 white_

RR

WW

RR RR

RRRR RRRR

RWRW RWRW

CODOMINANCECODOMINANCE

Codominance – Both alleles share dominance and are always expressed if present.

Ex: In chickens B = black feathers W = white feathers BW = black AND white feathers

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Cross a black (B) chicken with a white (W) chicken. Give the genotypic and phenotypic ratios.Key: B = black feathers WKey: B = black feathers W = white feathersCross: BB x WW

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W W

B

B

Genotypic Ratio:

Phenotypic Ratio:

Answer on next slide…

CODOMINANCECODOMINANCE

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BWBW

BWBW

BWBW

BWBW

BB

BB

WWW

Key: B = black W = whiteCross: BB x WW

Genotypic Ratio:0BB: 4BW: 0WW

Phenotypic Ratio:0 black: 4 black and white: 0 white

CODOMINANCECODOMINANCE

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Practice: Cross two black and white feathered chickens. Give the expected phenotypic and genotypic ratios of the offspring.

Key: __________________

Cross: _________________

Genotypic Ratio: ________________________

Phenotypic Ratio: ________________________

CODOMINANCECODOMINANCE

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Practice: Cross two black and white feathered chickens. Give the expected phenotypic and genotypic ratios of the offspring.

Key: B = black W = white

BW = black and white

Cross: _BW x BW__

Genotypic Ratio: __1BB: 2BW: 1WW_

Phenotypic Ratio: _1 black: 2 black and white: 1 white_

BB

WW

BB WW

BBBB BWBW

BWBW WWWW

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

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

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DIHYBRID CROSSDIHYBRID CROSS

Tracks the Tracks the inheritance inheritance ofof two traits two traits. . Ex. Ex. Seed shape and seed colorSeed shape and seed color

Each pair of alleles segregates Each pair of alleles segregates independentlyindependently during during gametegamete formationformation

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DIHYBRID CROSSDIHYBRID CROSS

Traits: Seed shape & Seed colorTraits: Seed shape & Seed color Alleles:Alleles: R round

r wrinkled Y yellow y green

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RrYy x RrYy

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

All possible gamete combinationsAll possible gamete combinations

DIHYBRID CROSSDIHYBRID CROSS

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RYRY RyRy rYrY ryry

RYRY

RyRy

rYrY

ryry

Gametes are placed in the punnett square

DIHYBRID CROSSDIHYBRID CROSS

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RYRY RyRy rYrY ryry

RYRY

RyRy

rYrY

ryry

Put R’s back together and Y’s back together

RRYY

Continue filling in the Punnett Square….

DIHYBRID CROSSDIHYBRID CROSS

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RRYY

RRYy

RrYY

RrYy

RRYy

RRyy

RrYy

Rryy

RrYY

RrYy

rrYY

rrYy

RrYy

Rryy

rrYy

rryy

RYRY RyRy rYrY ryry

RYRY

RyRy

rYrY

ryry

Genotypic Ratio:1 RRYY:2 RRYy:2 RrYY:1 RRyy:4 RrYy:2 Rryy:2 rrYy:1 rrYY1 rryy

DIHYBRID CROSSDIHYBRID CROSS

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RRYY

RRYy

RrYY

RrYy

RRYy

RRyy

RrYy

Rryy

RrYY

RrYy

rrYY

rrYy

RrYy

Rryy

rrYy

rryy

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

RYRY RyRy rYrY ryry

RYRY

RyRy

rYrY

ryry

If a pea plant with genotype RRYy (round, yellow peas) is crossed with a pea plant with genotype rrYy (wrinkled, yellow peas), what would the results be?

Key:

Cross:

Gametes:

Genotype:

Phenotype:19

OTHER PATTERNS OF INHERITANCE

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“Many genes” ; Many traits are controlled by more than one gene; have a variety of choices for expression.

Ex: _hair color, eye color, skin tone___

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Genes that have more than 2 alleles

Ex: blood group.

There are 3 possible alleles for this gene.

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