Lyon hypothesis

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Lyon hypothesis

[′lī·ən hī‚päth·ə·səs]
(genetics)
The concept that mammalian females are X-chromosome mosaics as a result of the random inactivation of one X chromosome in some embryonic cells and their descendant and of the other X chromosome in the rest.
References in periodicals archive ?
Causes are due to Lyonization, post-zygotic somatic mutations during early embryogenesis, gametic half-chromatid mutation occurring before fertilisation.
This phenotypic heterogeneity is due to lyonization, a process whereby one copy of the X-chromosome is randomly inactivated in all the cells of the female embryo, so that heterozygous females are essentially a "mosaic" of normal and mutant cells in varying proportions.
There is also evidence that, if one X contains abnormal genes, Lyonization may favour silencing that X over the normal one.
Symptomatic patients are almost exclusively male, but female carriers can be clinically affected due to unfavorable lyonization.
1) In females, lyonization results in functional mosaicism of X-linked genes, which is manifested by the Blaschkoid distribution of cutaneous lesions.
In a normal female cell, there are two copies of the X chromosome; however, only one copy is active, because the other copy is "silenced" through a process called X-inactivation or Lyonization.
Females generate both uTP-PCR and mTP-PCR melt peaks, due to Lyonization of their 2 X chromosomes.
X-inactivation studies, based on the phenomenon of lyonization, i.
Females may present if they are also unfortunate to present with lyonization.
8) The pattern of inactivation of the X chromosome in focal nodular hyperplasia, hepatic adenomas, and hepatocellular carcinomas, detected by assaying the DNA methylation patterns of the X-linked human androgen receptor gene (HUMARA), revealed that focal nodular hyperplasia demonstrates a random pattern of lyonization, consistent with a polyclonal reactive proliferation.
Increased susceptibility of a carrier of X-linked chronic granulomatous disease (CGD) to Aspergillus furnigatus infection associated with age-related skewing of lyonization.
The gp91-phox gene is located on the X chromosome, and carriers show a mosaic of nonpathogenic and defective cells, as our patient did, attributable to lyonization.