Question

Explain why all of the generation II females are carries for the red color gene

Answer 1

First of all, this pedigree is an x-linked dominant pedigree.

The dad has a genotype of
`X^(A)Y` (or whatever letter you choose to represent it) and since the mom is unaffected, she will be homo_zygous recessive or
`X^(a) X^(a)`. All the girls will receive the recessive allele from mom but the dad on the other hand can only pass on a dominant allele therefore all of the girls will become hetero_zygous with a genotype of
`X^(A) X^(a)`.