Problem 19

In mice, black color (B ) is dominant to white (b ). At a different locus, a dominant allele (A ) produces a band of yellow just below the tip of each hair in mice with black fur. This gives a frosted appearance known as agouti. Expression of the recessive allele (a ) results in a solid coat color. If mice that are heterozygous at both loci are crossed, what will be the expected phenotypic ratio of their offspring?

B = Black - dominant

A = Agouti - dominant

 

BbAa x BbAa =

Genotype

Phenotype
1

BBAA

agouti
2

BbAA

agouti
2

BBAa

agouti
4

BbAa

agouti
1

BBaa

black
2

Bbaa

black
1

bbAA

white
2

bbAa

white
1

bbaa

white

The phenotypic ratio is:

9 agouti: 4 white: 3 black