![]() ![]() ![]() A female will be affected with haemophilia only in the rare circumstance that she inherits mutated X chromosomes from both a haemophiliac father and a carrier or a haemophiliac mother. The daughter of a male haemophiliac will always inherit his mutation, while a son cannot ever inherit it. Each child of a carrier will have a 50% chance of inheriting their mother's mutation, of being a haemophiliac (sons) or carrier (daughters). If their sole X chromosome contains the haemophilia mutation they possess no second copy to provide for normal function, as in carrier females. Males possess only a single X chromosome, inherited from their mother, having received a Y chromosome from their father instead of a second X. Such a female, with normal clotting but possessing a single mutated copy of the gene, is called a carrier. A female who inherits a mutated copy on one X chromosome has also inherited a second X chromosome from the other parent that is likely to carry a non-mutated copy of the gene, capable of directing appropriate clotting. Females have two X chromosomes, and hence redundant copies of the blood clotting factor gene located on them. ![]() This is because the trait is recessive, meaning that only one correctly functioning copy of the blood clotting factor gene is necessary for normal clotting. The sex-linked X chromosome bleeding disorder manifests almost exclusively in males, even though the genetic mutation causing the disorder is located on the X chromosome and can be inherited from the mother by male children or from either mother or father by female children. ![]()
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