Question

When true breeding brown dogs are mated with certain true breeding white dogs, all of the F1 pups are white. The F2 progeny from some F1 x F1 crosses were 118 white, 32 black, and 10 brown pups. What is the genetic basis for these results?

Answer 1

Answer:

The results indicate that two independently assorting genes are involved (modified 9:3:3:1 ratio), with white blocking the expression of color by the other gene. The ratio of white : color pups is 3:1, indicating that the F.1 is heterogeneous (W/w). Among colored dogs, the ratio is 3 black : 1 brown, indicating that black is dominant to brown, and the F.1 is heterogeneous (B/b). The original brown dog is w/w ; b/b, and the original white dog is W/W ; B/B. The F.1 progeny are W/w ; B/b, and the F.2 progeny are: 12: 3: 1.

9 W/- ; B/-

3 W/- ; b/b

3 w/w ; B/-

1 w/w ; b/b

white

white

black

brown