When a yellow mouse was crossed to another yellow mouse, the F1 generation produces yellow and brown-black mice in the ratio 2 : 1. The yellow mice are never homozygous. The reason is
In some organisms, alleles in the homozygous state are harmful to the body. It is called Lethality and the genes are called Lethal genes. Eg: body colour of mice. In mouse, body colour yellow, in dominant homozygous condition is lethal to the body. It leads to the death of the body. A mouse with a heterozygous yellow body(Yy) is crossed with another mouse with a heterozygous yellow body(Yy), 4 types of progeny are obtained, in which one mouse is killed, because of lethality and remaining three mice are survived.
So, the correct option is ‘Homozygous yellow cannot survive due to the lethal effect of genes’.