Question

If a haemophilic man marries a carrier woman then which of the following holds true for their progenies?

• A. $50\%$ daughters are carrier and $50\%$ are haemophilic.
• B. All the daughters are haemophilic.
• C. All sons are haemophilic and all daughters are normal.
• D. All sons normal, all daughters carriers.

Answer 1

Answer: (A)

Haemophilia is an X-linked recessive disorder. The allele (h) which is responsible for haemophilia is present on the X chromosome and will be represented as $X^h$ . When a haemophilic man $X^{h}Y$ crosses with a carrier woman $X^{h}X$ the progeny produced will have two daughters and two sons. In the two daughters, one will be the carrier and one will be affected (haemophilic). In sons, one will be haemophilic and one will be normal. Hence, in progeny, total 50 percent will be a carrier and 50 percent will be haemophilic.
$Parents{X}^{h}Y(Haemophilicman)\times X^{h}X(Carrierwoman)Progeny{X}^h{X}^h(Haemophilicdaughter)X^{h}X(Carrierdaughter)X^{h}Y(Haemophilicson)XY(Normalson)$