Phenotypes in mice?

Question

In mice, the allele for black fur (B) is dominant over the allele for brown fur (b).

(b) What would be the genotypes and phenotypes of the parents (different mice!) if the offspring were born with a phenotypic ratio of 3 black to one brown?

Answer 1

Whenever you get this ratio, then both parents must be heterozygotes so Bb. The phenotypes of both would be black.

Bb x Bb gives BB Bb bB bb three black to one brown mouse.

Answer 2

Bb Bb