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.

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]

Lyon hypothesis

[lī′ən]
Etymology: Mary L. Lyon, English geneticist, b. 1925
a hypothesis stating that only one of the two X chromosomes in a female is functional, the other having become inactive early in development. Either the maternal or the paternal X chromosome may be inactivated in any given cell. Therefore an X-linked trait may be expressed by some cells and not by others.

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]

Lyon hypothesis

See X-INACTIVATION.

Lyon hypothesis

see INACTIVE-X HYPOTHESIS.

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

Lyon hypothesis

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.