Navigation Links
Lyon hypothesis


The Lyon hypothesis states that in cells with multiple X chromosomes, all but one is inactivated during mammalian embryogenesis. X-inactivation leads to clumped chromatin termed Barr bodies, which are generally considered inert. This formation of Barr bodies is called Lyonization.

In humans the X chromosome that is inactivated is determined by chance. In marsupials, however, the paternal X chromosome is always inactivated. Inactivation is achieved by methylation of the X chromosome DNA, a common way in which the cell silences particular genes. Certain animals have their coloring patters dictated by this phenomenon. For example, female Calico cats have unique patterns of fur due to certain areas where different X chromosomes are inactived. The X chromosomes that are activated express different coloring genes and lead to their mosaic fur color.

However, there are now reports that women still express many genes from their inactive X chromosomes, and that different women express different genes from the inactive X. Research by Carrel and Willard (2005) indicates that 15% of the genes on the inactive X chromosome are actually active across all women, and a further 10% of genes were switched on in some women.

The hypothesis was first stated by Mary F. Lyon in 1961 while she was studying the genetic consequences of radiation exposure, and therefore bears her name.

See also

Reference

  • Carrel L, Willard HF. X-inactivation profile reveals extensive variability in X-linked gene expression in females.. Nature 2005;434:400-404. PMID 15772666.
  • Lyon MF. Gene action in the X chromosome of the mouse (Mus musculus L). Nature 1961;190:372-373. PMID 13764598.

'"/>


(Date:10/15/2014)... , Oct. 15, 2014 Sandata Technologies, ... home and community-based care, today announced it released ... Sandata,s Santrax® Electronic Visit Verification™ Solution (EVV™)  for ... a home health company founded in 1996 and ... . The study details the ...
(Date:10/15/2014)... Researchers have linked increased resistance to bacterial pneumonia in ... sex hormone estrogen. , Females are naturally more resistant ... of scientists has shown that increased resistance to bacterial ... nitric oxide synthase 3 (NOS3). They also show that ... the female sex hormone estrogen. , The team, lead ...
(Date:10/14/2014)... Research shows SIRT6—a protein known to inhibit the ... of skin cancers by turning on an enzyme that ... , Previously considered protective, SIRT6 is part of a ... genomic stability and prevent some of the genetic flaws ... can lead to cancer. This study, in the journal,s ...
Breaking Biology News(10 mins):Sandata Announces Case Study with Quality Care Services, Inc. 2Two-faced gene: SIRT6 prevents some cancers but promotes sun-induced skin cancer 2
... global warming is causing the worldwide declines of amphibians ... to biologists. The findings, which contradict two widely held ... and toads and aid in their conservation. "We ... extinction event," said Peter Hudson, the Willaman professor of ...
... Greenland,s ice sheet Studies have indicated that ... increasing average summer air temperatures in southern coastal regions. ... mass from 1958 through 2008, Rignot et al. study ... sensing techniques; and surface mass balance, which is derived ...
... of DNA sequence information resulting from deciphering the human ... technological developments that have been vital in the identification ... for the development of novel genetic therapies to treat ... new genomic era heralds earlier diagnoses, greatly improved prevention ...
Cached Biology News:Global warming link to amphibian declines in doubt 2Global warming link to amphibian declines in doubt 3AGU journal highlights: Nov. 11, 2008 2AGU journal highlights: Nov. 11, 2008 3AGU journal highlights: Nov. 11, 2008 4AGU journal highlights: Nov. 11, 2008 5AGU journal highlights: Nov. 11, 2008 6AGU journal highlights: Nov. 11, 2008 7AGU journal highlights: Nov. 11, 2008 8AGU journal highlights: Nov. 11, 2008 9AGU journal highlights: Nov. 11, 2008 10Personalized medicine: Innovative online journal leads the way 2
Other biology definitionOther Tags