adj. describing genes (or the characteristics controlled by them) that are carried on the sex chromosomes, usually the *X chromosome. The genes for certain disorders, such as *haemophilia, are carried on the X chromosome; these genes and disorders are described as X-linked. Since most of these sex-linked genes are *recessive, men are more likely to have the diseases since they have only one X chromosome; women can carry the genes but their harmful effects are usually masked by the dominant (normal) alleles on their second X chromosome.
The way in which a characteristic or an illness determined by the SEX CHROMOSOMES in an individual’s cells is passed on to the succeeding generation. Men have one X and one Y sex chromosome and women have two X chromosomes. Disorders that result from an abnormal number of sex chromosomes include KLINEFELTER’S SYNDROME, which affects only men, and TURNER’S SYNDROME, which affects mainly women. Recessive GENES on the X chromosome cause most other sex-linked characteristics; in women these may well be masked because one of their two X chromosomes carries a normal (dominant) gene. In men, who have just one X chromosome, no such masking occurs – so more men than women are affected by X-linked characteristics or diseases. (See also HEREDITY.)... sex-linked inheritance
(XLP syndrome, Duncan’s disease) a hereditary disorder of the immune system caused by a defective *sex-linked gene carried on an *X chromosome. There is uncontrolled proliferation of B-*lymphocytes in response to infection by the Epstein-Barr virus, which can lead to fulminating hepatitis or lymphoma. This condition is due to a defect in a gene, SAP, which encodes a signalling molecule found in the cytoplasm of cells.... x-linked lymphoproliferative syndrome
Health Encyclopedia