Used to describe a characteristic or condition in which a mutation in a gene on the X chromosome causes the condition in males. Males have only one X chromosome, the other sex chromosome being a Y chromosome. A female has two X chromosomes. If she has one copy of the usual gene and one copy of the altered gene she is a carrier. Females who have only one copy of the altered gene most commonly do not show signs of the condition, but occasionally may, because of differences in X-chromosome inactivation.
Back to glossary index
