Question

In mice. Y is the dominant allele for yellow fur and y is the recessive allele for grey fur. Since Y is lethal when homozygous, the result of cross Yy × Yy will be

Answer 1

There will be 3 mice with yellow fur and 1 mouse with grey fur.

Since the result of Yy x Yy is:

YY , Yy , Yy , yy [ratio=3:1]

So YY, Yy, Yy are yellow mice and yy is a grey mouse.

Hope this helps!!:)

Answer 2

A lethal allele causes death of the organism.

Hence 2 yellow and 1 grey mouse will be former as YY bearing mouse will perish.

Cheers!