Question

Haemophilic female marries normal male, the theoretical ratio of their offsprings regarding haemophilia will be

• A. All offsprings are haemophilic.
• B. All girls are haemophilic.
• C. All sons are haemophilic.
• D. Half daughters and half sons are haemophilic.

Answer 1

The correct option is C All sons are haemophilic.

Haemophilia is a X-linked recessive disorder. One copy of the affected gene in males in each cell is sufficient to cause the disorder (X${}^h$Y). Females with two copies of the affected gene show the disorder (X${}^h$X${}^h$). Females heterozygous (X${}^h$X) for this trait are normal but serve as a carrier of the disease. According to the question, the female is haemophilic (X${}^h$X${}^h$) and father is normal (XY). The affected mother will inherit the disease to 100% sons (X${}^h$Y) while the 100% daughter will be normal but will serve as carrier. Correct answer is option C.
Parent generation : (X${}^h$X${}^h$) x XY

Gametes : (X${}^h$X${}^h$) --> XY	X${}^h$	X${}^h$
X	X${}^h$X carrier girl	X${}^h$X carrier girl
Y	X${}^h$Y haemophilic boy	X${}^h$Y haemophilic boy