Haemophilia is passed on as an allele in the X chromosome

Haemophilia is a blood condition that means bleeding does not stop. The bleeding occurs because the blood does not clot. People with hemophilia lack proteins in the blood that make scabs and blood clots. A person with a small cut or internal bleeding (bruise) could bleed to death. They do not bleed more than a normal person, but they bleed for much longer. The word comes from the Greek words haima ("blood") and philia ("to love"). To treat this, an affected person can get a blood donation from someone without hemophilia. The donor’s blood has clotting proteins and can temporarily make a normal scab. 30% of hemophilia A and B cases are the first person in their family to have hemophilia which is the result of an unexpected mutation (this means that there is an unexpected change in the body).