X-linked recessive genetic defects - how boys are affected
There are several X-linked (or sex-linked) recessive genetic disorders, (hemophilia, muscular dystrophy) which 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. Since male offspring receive their X chromosome from their mothers, the inheritance of a defect attached to that one copy of the X will cause the disorder.