The underlying pathology is a sex linked disorder ie the abnormal factor 8 or 9 gene carried on the X chromosome will transmit the disease. Since each male has only one copy of X chromosome from his mother, he will be affected if his X chromosome is abnormal. Unlike the male, each female has two copies of X-chromosomes (one from father and the other from mother) and though she will not be affected when one copy is abnormal, she will be a carrier and can pass down the gene to her children. However, there are very rare situations where both her copies are abnormal e.g. when the mother is a carrier and the father is a haemophiliac, or when there is a spontaneous mutation in the genes then a female hemophilia can occur. Thus in practice, almost all the hemophilia patients are male.
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