In mice, the allele for black fur is dominant to the allele for brown fur.

If a male homozygous black mouse is crossed with a female brown mouse, what percentage of the F2 offspring do you predict will be homozygous?

50%

Explanation:

The allele for black fur (B) is dominant to the allele for brown fur (b).

BB or Bb = black fur bb = brown fur

A male homozygous black mouse (BB) is crossed with a female brown mouse (bb). The male parent only produces B gametes and the female parent only produces b gametes. The F1 offspring will be 100% heterozygous Bb.

The F1 individuals will produce B and b gametes. If we cross the F1 individuals to each other (Bb x Bb), we'll get the following F2 offspring:

25% BB homozygous dominant 50% Bb heterozygous 25% bb homozygous recessive

So 50% of the F2 will be homozygous (BB or bb).