Why is haemophilia uncommon in human females?

Haemophilia is a sex linked recessive disorder carried on the X chromosome. A female has two X chromosomes, so she will suffer from the disease only if both of them carry the recessive gene. If only one X chromosome carries it, the normal dominant gene on the other X chromosome suppresses the disease and she remains a carrier. A male has only one X chromosome, so a single recessive gene expresses itself and he shows the disease. This is why haemophilia is uncommon in human females.