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INCOMPLETE DOMINANCE AND CODOMINANCE. 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. INCOMPLETE DOMINANCE. W. W. R. R. Cross a red (RR) snapdragon with a - PowerPoint PPT Presentation
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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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