Download Incomplete Dominance

Incomplete
Dominance
• Neither allele is dominant
• Heterozygotes are a blend
of homozygous phenotypes
= no distinct expression of
either allele
• F2 phenotypic and
genotypic ratios are 1:2:1
• Snapdragon/Four o’clock
flower color
• Eggplant color
• Tay-Sachs disease
Try these
• In a plant species, if the B allele (blue
flowers) and the W allele (white flowers) are
incompletely dominant (b is light blue), what
offspring ratio is expected in a cross between
a blue-flowered plant and a white-flowered
plant?
• What would be the phenotypic ratio of the
flowers produced by a cross between two
light blue flowers?
Codominance
• Both alleles are equally
dominant
• Heterozygotes express
both alleles = distinct
expression of the gene
products of both alleles
can be detected
• MN blood group
• F2 genotype and
phenotype ratios are
1:2:1
Genotype
Phenotype
LMLM
M
LMLN
MN
LNLN
N
Try These
1.
Cattle can be red (RR = all red hairs), white (WW
= all white hairs), or roan (RW = red & white hairs
together.
a. Predict the phenotypic ratios of offspring when a
homozygous white cow is crossed with a roan bull.
b. What should the genotypes & phenotypes for parent
cattle be if a farmer wanted only cattle with red fur?
2. A cross between a black cat & a tan cat produces
a tabby pattern (black & tan fur together).
a. What pattern of inheritance does this illustrate?
b. What percent of kittens would have tan fur if a tabby
cat is crossed with a black cat?