X Chromosome

The inherited package (or chromosome) of DNA that contains genes that help to determine the sex of an individual. Two X chromosomes are inherited by females and one X chromosome and one Y chromosome are inherited by males. Mutation of a gene found on the X chromosome can cause X-linked diseases.

Of the 23 pairs of chromosomes that humans carry in each cell of their body (except egg and sperm cells), genes on a single pair of chromosomes (called X and Y) determine gender. A female/woman can only give the X chromosome to her offspring (children), because females have two X chromosomes (XX), while males/men can give either an X or a Y chromosome to an offspring, because males have one X and one Y chromosome (XY). Importantly, the X chromosome also contains many genes that have nothing to do with determination of gender. Mutations in genes on the X chromosome result in diseases that are transmitted to male offspring (who have a single X-chromosome) only from their biological mother (maternal inheritance), or to female offspring from their mother or father (maternal or paternal inheritance). These are called X-linked diseases. In most cases, male offspring are affected by X-linked disease while females may either be unaffected carriers or may be affected with an X-linked disease.