Question

If the father shows normal genotype and mother shows a carrier trait for haemophilia
A. All the female offspring will be normal
B. All the female offspring will be carriers
C. A male offspring has 50% chances of active disease
D. Both A and C

Answer 1

Hint: Haemophilia is an X linked recessive disorder. Genes for haemophilia are located on the X chromosome and mutation in these genes causes haemophilia which affects clotting factors and causes prolonged bleeding.

Complete answer: If the father shows normal genotype and mother shows a carrier trait for haemophilia, a male offspring has 50% chances of the active disease. Haemophilia is a genetic disease that affects the blood clotting ability in individuals. It is caused by a mutation on the X chromosome. Genes for haemophilia are located on the X chromosome. Haemophilia is an X linked recessive disorder. In the above question, the father is normal (XY) and the mother is a carrier (XXh). Gametes produced by the male has an X chromosome and a Y chromosome. Gametes produced by the female has an X chromosome and Xh chromosome. When the male gamete having X chromosome fuses with the female gamete having X chromosome, it leads to a normal female. When the male gamete having X chromosome fuses with the female gamete having the Xh chromosome, it leads to a carrier female (XXh). When a male gamete with a Y chromosome fuses with the female gamete having an X chromosome, it leads to a normal male, but when male gamete having Y chromosome fuse with female gamete having Xh chromosomes it leads to haemophilic male. There are two types of haemophilia:
i. Haemophilia A: It occurs due to a mutation in factor VIII gene on the X chromosome.
ii. Haemophilia B: It occurs due to a mutation in factor IX gene on the X chromosome.
Major symptoms of haemophilia are as follows:
i. Bleeding in gums or teeth.
ii. Bleeding in joints which influences knee and elbow.
iii. Bleeding in skin or muscle.
Hence, the correct answer is option C.

Note: Normal genotype male and carrier female can give birth to children having 4 genotypes namely normal female (XX), carrier female (XXh), normal male (XY) and haemophilic male (XhY). Haemophilia A affects about 1 in 5,000 to 10,000, while haemophilia B affects about 1 in 40,000, males at birth.