Question

A normal woman has a haemophilic son besides three normal daughters. The genotypes of the woman and her husband
with respect to haemophilia would respectively be:

• A. $XX,X^{h}Y$
• B. $X^{h}X,X^{h}Y$
• C. $X^h{X}^h,XY$
• D. $X^{h}X,XY$

Answer 1

The correct option is D $X^{h}X,XY$

Haemophilia is X linked recessive genetic disorder. Son is haemophilic only when the mother has gene for haemophilia. As mentioned in the question, mother is normal and son is haemophilic, it means mother is a carrier. Hence, the genotype of mother is X${}^h$ X.

As mentioned in the question, daughters are normal and it is possible only when father is non haemophilic. Hence, the genotype of father is XY. (If father was haemophilic, as mother is carrier, there is a chance for daughters to be haemophilic).