Incomplete Dominance: The heterozygous genotype produces a phenoytype that falls in between the dominant trait and the recessive trait.
Incomplete Dominance
Example:
In flowers, petal color demonstrates incomplete dominance. Red results when a flower has homozygous dominant alleles for the trait. White results when a flower has homozygous recessive alleles for the trait. A flower that is heterozygous for this trait will be pink. Predict the genotypic and phenotypic ratios of the offspring for the following:
Rr Rr
Rr Rr
Genotypic Ratio:
100% Rr
Phenotypic Ratio:
100% pink flowers
1. Red and white RR x rr
R R
r
r
Example:
In flowers, petal color demonstrates incomplete dominance. Red results when a flower has homozygous dominant alleles for the trait. White results when a flower has homozygous recessive alleles for the trait. A flower that is heterozygous for this trait will be pink. Predict the genotypic and phenotypic ratios of the offspring for the following:
RR RR
Rr Rr
Genotypic Ratio:
50% RR 50% Rr
Phenotypic Ratio:
50% Red flowers, 50% Pink flowers
2. Red and pink RR x Rr
R R
R
r
Rr Rr
rr rr
Genotypic Ratio:
50% Rr 50% rr
Phenotypic Ratio:
50% Pink flowers 50% White flowers
Genotypic Ratio:
25% RR 50% Rr 25% rr
Phenotypic Ratio:
25% Red flowers 50% Pink flowers 25% White flowers
RR Rr
Rr rr
White and Pink rr x Rr
r r
R
r
Pink and Pink Rr x Rr
R r
R
r
Codominance
Codominance: condition in which both alleles of a gene are expressed in heterozygous offspring.
Example 1:
In cows black coat color and white coat color are codominant. Heterozygous offspring will be spotted.
1. Black cow and White cow BB x WW
BW BW
BW BW
B B
W
W
Genotypic Ratio:
100% BW
Phenotypic Ratio:
100% Spotted cow
Example 1:
In cows black coat color and white coat color are codominant. Heterozygous offspring will be spotted.
2. Black cow and Spotted cow BB x BW
BB BB
BW BW
B B
B
W
Genotypic Ratio:
50% BB 50% BW
Phenotypic Ratio:
50% Black cow 50% Spotted cow
Example 1:
In cows black coat color and white coat color are codominant. Heterozygous offspring will be spotted.
3. Both Spotted cows BW x BW
BB BW
BW WW
B W
B
W
Genotypic Ratio:
25 % BB 50% BW 25% WW
Phenotypic Ratio:
25% Black cow 50% Spotted cow 25% White cow
Example 2:In blood typing, the gene for type A and the gene for type B are codominant. The gene for type O is recessive.
Blood Type (phenotype) Genotype
A AA or AO
B BB or BO
AB AB
O OO
Determine the possible blood types of the offspring when:
1. Mother is type O, Father is type A (homozygous)
AO AO
AO AO
O O
A
A
Genotypic Ratio:
100% AO
Phenotypic Ratio:
100% Type A Blood
Determine the possible blood types of the offspring when:
AA AB
AO BO
A B
A
O
Genotypic Ratio:
25 % AA 25% AO 25% AB 25% BO
Phenotypic Ratio:
50% Type A Blood 25% Type AB Blood 25% Type B Blood
2. Mother is type AB, Father is Type A (heterozygous)
Determine the possible blood types of the offspring when:
AB BO
AO OO
A O
B
O
Genotypic Ratio:
25 % OO 25% AO 25% AB 25% BO
Phenotypic Ratio:
25% Type O Blood 25% Type A Blood 25% Type AB Blood 25% Type B Blood
3. Mother is type A (heterozygous), Father is type B (heterozygous)
Determine the possible blood types of the offspring when:
AB AB
AB AB
B B
A
A
Genotypic Ratio:
100% AB
Phenotypic Ratio:
100% Type AB Blood
4. Mother is type B (homozygous), Father is type A (homozygous)
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