In mice, a gene controlling coat colour has 2 alleles; B (black) and b (white). A pure breeding black mouse is crossed to a white mouse and all the offspring are black. The offspring are then crossed to white mice. The phenotypes of the offspring of this second cross are expected to be
A) all black
B) 3/4 black, 1/4 white
C) 1/2 black, 1/2 white
D) 1/4 black, 3/4 white
E) all white

Question

Quizplus · Accepted Answer

Since the first cross between a pure breeding black mouse (BB) and a white mouse (bb) results in all black offspring, these offspring must be heterozygous (Bb). When these heterozygous black mice (Bb) are crossed with white mice (bb), the expected offspring ratio is 1/2 black (Bb) and 1/2 white (bb), following Mendelian inheritance principles.

In Mice, a Gene Controlling Coat Colour Has 2 Alleles;