Answer:
There are several X-linked (or sex-linked) recessive genetic disorders, (hemophilia, muscular dystrophy) that are inherited through a genetic defect on an X chromosome. A female has 2 X chromosomes, one she inherited from her mother and one she got from her father. A male has an X chromosome from his mother and a Y chromosome from his father. If a woman has the defect on one of her X chromosomes, and the father's X chromosome is normal, there is a 25% chance for each pregnancy to produce:
An unaffected girl
A girl who carries the defect
An unaffected boy
A boy with the disorder