Question

A woman with color-normal vision, but whose father was color blind, marries a man with normal vision. They are expecting a child. They learn through genetic testing that their child will not be color blind. What is the probability that their child is a boy?

Answer 1

To know what happens here, you need to analyze the alleles.

If the father is color blind and the daughter is not, you can suppose that is a recessive allele.

You can tell she is a carrier only, and because we received one sexual allele from each parent. If they ask you about the gender, we can suppose a cross between Xx and XY being lower x the recessive allele (color-blind vision).

When you draw the Punnett square, you'll found the probabilities are XX, XY, Xx, and xY.

So, you have a 50% chance of having a boy and 25% chance of having a color-blind boy.