Question

Mary’s father has haemophilia but her husband is also haemophilic. What is the chance of her daughter having this disease?
A)0%
B)50%
C)100%
D)25%

Answer 1

Hint: Haemophilia is a genetic disorder in which the body is unable to form blood clots and cannot stop bleeding. In this disorder, the bleeding does not stop and the person is in risk of bleeding inside the joints. It is due to the mutation in clotting factor VIII or IX gene. It is a X-linked chromosome disease.

Complete answer:
To solve this question, we must know about the gene representation in haemophilia.

According to the question, Mary’s father was haemophilic. The gene of Mary is represented as XhX. As the X chromosome is transferred from the father to daughter. The daughter would be the carrier of haemophilia but will not have any phenotypic effect.

Mary’s Husband is haemophilic. So, its gene would be represented as XhY.
The cross between Mary and her husband will produce offsprings-

	Xh	X
Xh	XhXh (haemophilic daughter)	XhX (Carrier daughter)
Y	XhY (haemophilic son)	XY (Normal Son)

The son will be haemophilic if only a single X haemophilic gene is present. The daughter will be the carrier if the father is haemophilic. The daughter will only be haemophilic if both the X gene has haemophilia genes. This only happens if the mother is the carrier.
Out of two daughters, one is haemophilic and the other is the carrier.

Hence, the correct answer is option (B)

Note: Haemophilia is a very rare disease. It is not curable but can be treated. The most common form of haemophilia is haemophilia A. The males are mostly affected by it. However, it is very rare in females.