I need help working out this question woman has normal visi

I need help working out this question .
woman has normal vision although her maternal grandfather (her mother’s father) had red- green colorblindness, a sex-linked recessive trait. Her maternal grandmother and the woman’s own father are assumed to not possess a copy of the mutant allele. The woman marries a man with normal vision although his father was colorblind. What is the probability that the first child of this couple will be colorblind?

Solution

As it is x linked inheritance, the genotype of women is either xx = Normal or xxc =Carrier for disease. If she is carrier (xxc) and married normal man, then the probability of 1st chaild getting colour blindness is 1/4 = 0.25

Color blind ness is x linked and it inherit criss cross manner. That mean, male transfer color blindness to her female children and. female transfer her male children.

XXc x XY ----------------> XX, XY, XXc & XcY

XcY progeny is only colour blind. So probability is 1\\4