Question

Next, you perform a cross with a mouse with black fur and a mouse with white fur. Which result(s) for the offspring would confirm that the mouse with black fur was heterozygous?

4 mice with black fur

8 mice with black fur, 1 mouse with white fur

5 mice with black fur, 6 mice with white fur

6 mice with black fur, 2 mice with white fur

Answer 1

Answer: 5 black, 6 white.

Reason: White is recessive, so a heterozygous black (Bb) crossed to a white (bb) gives a 1:1 phenotypic ratio (Bb : bb → black : white). 5 black and 6 white fits that expectation. (8 black, 1 white is possible by chance from a 1:1 cross but is unlikely; 4 black only implies the black parent was BB.)