Question

In Labrador retrievers, black coat color (B) is dominant to brown (b). Suppose that a black Lab is mated with a brown one and the offspring are 4 black puppies and 1 brown. What can you conclude about the genotype of the black parent?

Answer 1

According to question,

In Labrador retrievers, black coat color (B) is dominant to brown (b), which means brown is recessive

Now, there are ONLY ONE possibilities of crosses when black Lab mate with brown Lab to reproduce atleast one black and one brown puppies. Bb - black, bb - brown

I) Bb X bb = Bb, Bb, bb, bb (BLACK:BROWN = 2:2)

The ratio of getting black and brown puppies from cross (I) is (2:2).

$\therefore$ We can conclude that the genotype of black parent is (Bb)