Dec 3

Colorblindness is an x-linked recessive trait in humans. A color-blind mother and a father with normal vision have a daughter. Is she colorblind? That daughter marries a color-blind man and they have two children, a boy and a girl. What is the probability that those children are color-blind?

Both the son and the daughter have 50% chance of being color-blind.

The color-blind mother must be X^cX^c and the normal father must be X⁺Y. The daughter (who gets one X from mom and one X from Dad) must be X^cX⁺. The Color-blind man is X^cY. SO, X^cX⁺ x X^cY gives daughters who are 50% X⁺X^c and 50% X^cX^c and gives sons who are 50% X⁺Y and 50% X^cY.