Any part of the DNA that controls an inherited trait is called a gene. Examples of inherited traits are eye color, hair color and blood type. Genes are present within the cell in packages called chromosomes. Most of the body's cells contain a complete copy of chromosomes and their genes. X and Y. Males receive an X chromosome from their mother and a Y chromosome from their father.
Females have two X chromosomes, one from each parent.
The genes that control production of clotting factors VIII and IX are located in the X chromosome. Not all males with hemophilia have mothers who are carriers. Sons of women who carry the hemophilia gene have a 50 percent chance of inheriting hemophilia. Daughters of women who are carriers have a 50 percent chance of also being carriers of hemophilia. In families where only one male is known to have hemophilia, it can be hard to determine whether the hemophilia gene was passed from a mother who carries the gene, or whether a new mutation occurred in the person with hemophilia.