Hemophilia is an inherited disorder, passed from parent to child. It is caused by a defective gene located on the X chromosome.17 As a result, the disorder occurs primarily in males. Females carry two copies of the X chromosome, so if one chromosome is defective, the other can compensate. Males, however, carry only one X chromosome, so if the chromosome is defective, they have the disease.
Women with one defective chromosome (X) are carriers of the hemophilia trait. The sons of female carriers have a 50% chance of having hemophilia. Daughters of female carriers have a 50% chance of also being carriers of hemophilia.
All daughters of men with hemophilia will be carriers of the trait.17
