Question

Two forms of hemophilia are determined by genes on the X chromosome in humans. Assume that a phenotypically normal woman whose father had hemophilia is married to a normal man. If their first child is a son, what is the probability that their first son will have hemophilia

Answer 1

The probability is 1/4 or 25% chance of having haemophilia

Explanation:

Let's take the hemophilia gene to be 'a' and normal to be 'A'. The woman has a gene for hemophilia due to inheritance from the father. She then married a normal man. Thus when we do our genotypic crossing, there is a product of XAXA, XAY, XAXa, XaY. Thus an hemophiliac male, XaY is just 1/4 probability