Male pattern baldness has been studied and is not completely understood, however, it is thought to be a sex-linked disorder. Since females have two X chromosomes and males have one, a son who is XY would inherit the X from his mother and the Y from his father. The mother passes one of her two X chromosomes to her son. If the X she passes down came from the maternal grandfather and had linked to it a gene for baldness, it was thought that the son would become bald as an adult. If there is a variant gene for the androgen receptor on the X chromosome, there is a likelihood of male pattern baldness occurring in the male, since males only inherit one X chromosome. However, there is an additional gene on chromosome 20 involved in baldness. Even though in the past, one would look to the mother's father to see if he were bald or not, both parents genetics have an effect on the son.