Question

Haemophiliac man marries a normal homozygous female. The probability of their child being haemophiliac?
A. 0.00%
B. 25%
C. 50%
D. 75%

Answer 1

Hint: Haemophilia is the inherited genetic disorder found in men which lessens the body’s ability to make blood clots due to the absence of clotting factor. This results in excessive blood loss both internal and external in people after injury. It causes bruises and the risk of bleeding inside the brain or joints increases.

Complete answer:
- Haemophilia is also known as Bleeder's disease. It is the genetic disorder that is inherited from parents to the child.
- The genes that are associated with haemophilia are located on the X chromosomes. Males have the genotype XY with one X chromosome and females have genotype XX with two X chromosomes.
- In males, in each cell, only a single copy of an altered gene is enough to cause haemophilia. Let us now consider the given situation.
A haemophiliac man has a genotype - X*Y (recessive X chromosome)
A normal homozygous female has a genotype - XX
The inheritance pattern of the offsprings is shown below.

In this scenario, the sons will receive the normal X chromosome from the mother and Y chromosome from the father so they are normal and do not have any recessive gene that causes haemophilia. Whereas the daughters will receive the normal X chromosome from the mother and a recessive X* chromosomes from the father so they will be the carrier of haemophilia.

Therefore the correct option is (A) 0.00%.

Note: Haemophilia is also known as Royal disease as the gene was passed from Queen of England, Queen Victory to the ruling families of Spain, Russia and Germany. There are three types of haemophilia. They are three types of haemophilia. Lack of clotting factor VIII causes haemophilia A, deficiency of clotting factor IX causes haemophilia B and deficiency of clotting factor XI haemophilia C.