If a gene is X-linked, it appears on the X chromosome and not on the Y chromosome. Diseases that result from an abnormal recessive X-linked gene usually develop only in males. This is because males have only one X chromosome.
Females have two X chromosomes, so they usually receive a normal gene on the second X chromosome.
The normal gene is dominant, preventing females from developing the disease. If the father has an abnormal recessive gene on his X chromosome and the mother has two normal genes, all of their daughters receive one abnormal gene and one normal gene, making them carriers. None of their sons receive the abnormal gene. If the mother is a carrier and the father has the normal gene, any son has a 50 percent chance of receiving the abnormal gene from the mother. All rights reserved.