Question

Why is haemophilia uncommon in females?

Answer 1

The X chromosome carries the recessive sex-linked gene h, which causes haemophilia. Females become haemophilic only when both X chromosomes carry the gene (X^hX^h). Females with only one haemophilia allele (XX^h) appear normal. Female haemophilia is extremely rare, as it requires a homozygous recessive gene for the condition.