er mother and one from her father. A female with a hemophilia allele on one X chromosome usually has a normal allele on her other X chromosome that can produce normal clotting factor. The normal allele provides some protection against having hemophilia. A female with one hemophilia allele and one normal allele is called heterozygous, or a carrier. Some girls and women who are heterozygous have bleeding symptoms. While bleeding symptoms in females are usually milder than those in males with hemophilia, in rare cases, a female who is heterozygous can have bleeding symptoms that are as serious as those of a male with hemophilia. A female can also have hemophilia if (a) she inherits hemophilia alleles from both of her parents or (b) if she inherits one hemophilia allele and her other X chromosome is missing or does not work properly. Females with these types of inheritance patterns are as likely as males with hemophilia to have severe bleeding symptoms. Because most females who inherit hemophilia are heterozygous and have no bleeding symptoms or mild bleeding symptoms, hemophilia may be hidden in a family for many generations if it passes only through females. If a mother is heterozygous for hemophilia and the father does not have hemophilia, each son has a 1 in 2 (50%) chance of getting his mother's hemophilia allele and having hemophilia. Each daughter has a 1 in 2 (50%) chance of getting her mother's hemophilia allele and being heterozygous. Overall, there is a 1 in 4 (25%) chance for each pregnancy that the baby will be a son with hemophilia and a 1 in 4 (25%) chance that the baby will be a heterozygous daughter. There is a 1 in 2 (50%) chance that the baby (either a son or a daughter) will not get the hemophilia allele at all and, therefore, can't pass it down to his or her children. View Larger Download Diagram of hemophilia inheritance from a mother who is a carrier Diagram of hemophilia inheritance from a mother who is a carrier A father who has hemophilia passe