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