Question Detail
Question
Mary's father has haemophilia, an X-linked recessive trait, but her husband does not. What is the chance that her son will have the disease?
Correct Answer
Option C is the correct answer.
Detailed Explanation
Mary's father has haemophilia (XhY). He passed his Xh chromosome to Mary. Mary's husband is normal (XHY). Mary is therefore a carrier (XHXh). The chance that Mary passes her Xh to a son is 1/2. If a son gets that Xh, he will be haemophilic (XhY). So the chance is 50% for each son.
Hint
Mary is a carrier, and sons get their X from her.