Question

If 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. Female offspring has probability of 50% to have active disease.

Answer 1

Answer: (C)

A male offspring has 50% chances of active disease.

Answer 2

Haemophilia is a sex-linked recessive disease, which shows its transmission from unaffected carrier female to some of the male progenies, hence shows criss - cross inheritance pattern. It is genetically due to recessive sex - linked gene h carried by X chromosome. A female becomes haemophiliac only when both its X chromosomes carry the gene$(X^h X^h)$ whereas in case of males, a single gene for the defect is able to express itself $(X^h Y)$. If father is normal (X Y) and mother is carrier $(X^h X)$ then the probabilities for active disease in offsprings are illustrated in the cross given below:
Hence, a male offspring has 50% chance of active disease,