Question

Hemophilia (Xh) is recessive to normal blood clotting (XH) and is sex-linked. A non-hemophilic man and a non-hemophilic woman have children together. Both of the couple’s respective fathers were hemophiliacs.
a. What proportion of the couple’s offspring will be hemophiliacs?

b. What proportion of the daughters will be carriers of the Xh allele?

Answer 1

The Male has one X-chromosome and one Y chromosome. Female has two copies of X-chromosomes. The male receives his X chromosome from his mother and Y chromosome from his father. The Female receives one X-chromosome from her father and one from mother.

Given that father of females had hemophilia. It means that female has one copy of hemophilic allele and a copy of the normal allele.

So the genotype of the female is XhXH and the genotype of the male is XHY.

A - Out of four children, only one will be affected by hemophilia. So, the proportion of affected children is 1/4.

Out of two daughters, one daughter has one allele of hemophilia and one normal allele and one daughter has both normal alleles. So the proportion is 1/2.

So 1/2 of the daughter will be a carrier for hemophilia.