Q. A woman with normal vision whose mother was colourblind marries a man with normal vision. The woman is pregnant with her first child. What is the probability that the child will be a colour blind boy?

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Solution:

The mother of the woman was color blind (XcXc). The normal vision woman will have XXc. The normal vision man will have XY. Their marriage can produce 4 possible offsprings: XX (daughter with normal vision), XcX (carrier daughter with normal vision), XY (son with normal vision) and XcY (colorblind son). Thus, there is one in four chance that the child will be a colorblind boy.