Explain the pattern of inheritance of haemophilia in humans. Why is the possibility of a human female becoming a haemophilic is extremely rare? Explain.

Explanation

Haemophilia is a sex linked disease present on recessive X chromosome. For a daughter to be haemophilic mother should be a carrier and father should be haemophilic. A female becomes haemophilic only when both its X chromosomes carry the gene. However, such females generally die before birth because the combination of these two recessive alleles is lethal. If the gene is present on one X chromosome, then the female appears normal. Hence, it is very rare for a female to be haemophilic.