Lyon hypothesis


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Lyon hypothesis

 [li´on]
the random and fixed inactivation (in the form of sex chromatin) of all X chromosomes in excess of one in mammalian cells at an early stage of embryogenesis, leading to mosaicism for X-linked genes in the female, since the paternal X chromosome is inactivated in some cells and the maternal one in the remainder.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

ly·on·i·za·tion

(lī'on-i-zā'shŭn),
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.
See also: gene dosage compensation.
[M. Lyon]
Farlex Partner Medical Dictionary © Farlex 2012

ly·on·i·za·tion

(lī'on-ī-zā'shŭn)
The normal phenomenon whereby 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. Its randomness explains the more variable expressivity of X-linked traits in women than in men.
See also: gene dosage compensation
Synonym(s): Lyon hypothesis, X-inactivation.
[M. Lyon]
Medical Dictionary for the Health Professions and Nursing © Farlex 2012

Lyon hypothesis

See X-INACTIVATION.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005

Lyon hypothesis

see INACTIVE-X HYPOTHESIS.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005

Lyon,

Mary F., English cytogeneticist, 1925–.
Lyon hypothesis - Synonym(s): lyonization
lyonization - 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. Synonym(s): Lyon hypothesis; X-inactivation
Medical Eponyms © Farlex 2012