Question

Haemophilic carrier female marries a normal man. In her progeny.

• A. All daughters will have haemophilia
• B. All sons will have haemophilia
• C. $50\%$ daughters will have haemophilia
• D. $50\%$ sons will have haemophilia

Answer 1

Answer: (D)

$50\%$ sons will have haemophilia

A daughter would have a 50% chance of becoming a carrier, but not actually a sufferer of the disease. This happens because a female has two X chromosomes, and since the father can only ever give an unaffected X chromosome the only possible outcomes will be that the daughter will either have two normal X chromosomes or one affected X paired with a normal X chromosome. A female would need two affected X chromosomes in order to become a hemophiliac because the gene is recessive and a normal chromosome would override it. On the other hand, a son would have a 50% chance of suffering from the disease. This happens because a male has an X chromosome, which he’d receive from the mother, paired with a Y chromosome, which he’d receive from the father. The mother has a 50% chance of giving her affected X chromosome and since there won’t be another normal X chromosome to be paired with it, there will be nothing to override the trait.

So, the correct answer is '50% sons will have haemophilia'.