Incomplete Dominance: The heterozygous genotype produces a phenoytype that falls in between the dominant trait and the recessive trait.

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Incomplete Dominance
Incomplete Dominance The heterozygous genotype
produces a phenoytype that falls in between the
dominant trait and the recessive trait.
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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
1. Red and white RR x rr
Genotypic Ratio 100 Rr Phenotypic Ratio 100
pink flowers
R R
Rr Rr
Rr Rr
r r
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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
Genotypic Ratio 50 RR 50
Rr Phenotypic Ratio 50 Red flowers, 50 Pink
flowers
2. Red and pink RR x Rr
R R
RR RR
Rr Rr
R r
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White and Pink rr x Rr
Genotypic Ratio 50 Rr
50 rr Phenotypic Ratio 50 Pink flowers
50 White flowers
r r
Rr Rr
rr rr
R r
Pink and Pink Rr x Rr
Genotypic Ratio 25 RR
50 Rr 25 rr Phenotypic
Ratio 25 Red flowers 50 Pink flowers
25 White flowers
R r
RR Rr
Rr rr
R r
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Codominance Codominance condition in which both
alleles of a gene are expressed in heterozygous
offspring.
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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

B B
Genotypic Ratio 100 BW
Phenotypic Ratio 100 Spotted cow
BW BW
BW BW
W W
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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
B B
Genotypic Ratio 50 BB 50 BW
Phenotypic Ratio 50
Black cow 50 Spotted cow
BB BB
BW BW
B W
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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
Genotypic Ratio 25 BB 50 BW
25 WW
Phenotypic Ratio 25 Black cow
50 Spotted cow 25 White cow
B W
BB BW
BW WW
B W
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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
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Determine the possible blood types of the
offspring when
1. Mother is type O, Father is type A (homozygous)
O O
Genotypic Ratio 100 AO
Phenotypic Ratio 100 Type A Blood
AO AO
AO AO
A A
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Determine the possible blood types of the
offspring when
2. Mother is type AB, Father is Type A
(heterozygous)
Genotypic Ratio 25 AA 25 AO 25 AB
25 BO Phenotypic
Ratio 50 Type A Blood 25 Type AB Blood
25 Type B Blood
A B
AA AB
AO BO
A O
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Determine the possible blood types of the
offspring when
3. Mother is type A (heterozygous), Father is
type B (heterozygous)
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
A O
AB BO
AO OO
B O
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Determine the possible blood types of the
offspring when
4. Mother is type B (homozygous), Father is type
A (homozygous)
B B
Genotypic Ratio 100 AB
Phenotypic Ratio 100 Type AB Blood
AB AB
AB AB
A A