Question Detail
Question
Haemophilia is caused by a sex-linked, recessive allele. Two parents have a haemophilic son, a normal son and a haemophilic daughter. What are the most likely genotypes of the mother and father respectively? A. XHXh and XhY B. XHXh and XHY C. XhXh and XHY D. XHXH and XhY
Correct Answer
Option A is the correct answer.
Detailed Explanation
They have a haemophilic daughter. For a daughter to be haemophilic (XhXh), she must inherit an Xh from both parents. The father must be haemophilic (XhY) to pass an Xh to a daughter. The mother must be a carrier (XHXh) to pass an Xh to both the haemophilic son and daughter. This cross (XHXh x XhY) can produce: XHXh (carrier daughter), XhXh (haemophilic daughter), XHY (normal son), XhY (haemophilic son).
Hint
A haemophilic daughter requires a haemophilic father.