Sex-linked diseases are passed down through families through one of the X or Y chromosomes. X and Y are sex chromosomes.
inheritance occurs when an abnormal gene from one parent causes disease
even though the matching gene from the other parent is normal. The
abnormal gene dominates.
But in recessive inheritance, both
matching genes must be abnormal to cause disease. If only one gene in
the pair is abnormal, the disease does not occur or it is mild. Someone
who has one abnormal gene (but no symptoms) is called a carrier.
Carriers can pass abnormal genes to their children.
The term "sex-linked recessive" usually refers to X-linked recessive.