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Medical Term:


Pronunciation: li'on-i-za'shun

Definition: The normal phenomenon that wherever there are two or more haploid sets of X-linked genes in each cell all but one of the genes are inactivated apparently at random and have no phenotypic expression. Lyonization is usual but not invariable for all loci. Its randomness explains the more variable espressivity of X-linked traits in women than in men. Lyonization occurs in men with the Klinefelter (XXY) karyotype.

Synonym(s): Lyon hypothesis, X inactivation, X-inactivation

[M. Lyon]

See Also: gene dosage compensation

© Copyright 2016 Wolters Kluwer. All Rights Reserved. Review Date: Sep 19, 2016.