In mice, black fur (B) is
dominant over brown fur (b). Breeding a
a homozygous black mouse produces all black offspring.
a. What is the genotype of the gametes produced
by the brown-furred parent?
b. What is the genotype of the brown-furred
c. What is the genotype of the black furred
d. What is the genotype of the black-furred
flower color is governed by two alleles, but
neither allele is truly dominant over the other. Petunias with the genotype R R are red-flowered, those that are heterozygous
(R W ) are pink, while those with the (WW ) genotype have white flowers. This is an example of incomplete dominance.
If a white-flowered plant is crossed with a red-flowered plant, what is
the genotypic ratio of the F1?
What is the phenotypic ratio of the F1?
c. If two of the F1 offspring were crossed,
what phenotypes would appear in the F2?
d. What would be the genotypic ratio in the
MONOHYBRID PROBLEMS ILLUSTRATING CODOMINANCE
Another type of monohybrid
inheritance involves the expression
of both phenotypes in the heterozygous situation. This is called
One of the best known examples of codominance occurs in the blue
Andalusian chicken. “Blue”
birds are heterozygous (BW) and result from the mating between a black bird
(BB) and a white bird (WW). Blue birds
do not really have blue feathers, instead having a mixture of black and white feathers that reflects
light to appear blue. Thus, the “blue” coloration is not a
consequence of blending of the pigments (after all, the mix is not gray) but
rather the result of both colors existing on the same bird. That is both phenotypes occur on the same
If a blue Andalusian hen is mated with a white rooster, what will be the
genotypic and phenotypic ratios in the F1 generation?
Genotypic ratio ________________________________________
Phenotypic ratio _______________________________________
List the parental genotypes of crosses that could produce at least some:
white offspring _______________________________
black offspring ________________________________________