Question

What is Haemophilia? Write its sex-linked inheritance pattern.

Answer 1

Haemophilia is a disorder in which blood clotting factors (factor VII or IX) are not produced sufficiently and hence the blood fails to clot. As a result there is easy bruising and blood clotting does not occur after an injury. It is a sex linked recessive disorder. The associated genes are found to be present in the X chromosome. So, it is more common in males than in female. Since males have a single X chromosome, if it is affected they will have the disease. In females however both the X chromosomes will need to be affected for them to have the disease. If only one X chromosome is affected in females than the other X chromosome will show a dominant effect and she will only be a carrier and will not be affected.