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:9/29/2014)... from the skeleton of a man who lived 2,330 years ... ourselves as humans? A great deal when his DNA profile ... terms found to-date in a region where modern humans ... , The man,s maternal DNA, or ,mitochondrial DNA, was sequenced ... Mitochondrial DNA provided the first evidence that we all come ...
(Date:9/29/2014)... -- NXT-ID, Inc. (Nasdaq: NXTD and ... focused on the growing mobile commerce market, today announced ... the Company,s Vice-President and Chief Financial Officer effective immediately. ... Financial Officer. Mr. Pereira will continue to serve as ... Mr. Miceli, age 56, has extensive hands ...
(Date:9/29/2014)... were able to safely tolerate treatment with cells cultured ... today in the journal Multiple Sclerosis and Related ... its kind, was conducted by researchers at Mount Sinai, ... at several other institutions. , While designed to ... data also suggested that a preparation of cultured cells ...
Breaking Biology News(10 mins):Ancient human genome from southern Africa throws light on our origins 2Ancient human genome from southern Africa throws light on our origins 3NXT-ID, Inc. Names Vice-President and Chief Financial Officer 2NXT-ID, Inc. Names Vice-President and Chief Financial Officer 3Cells from placentas safe for patients with multiple sclerosis 2
... A team led by the University of Colorado Boulder has been ... Energy to research modifying E. coli to produce biofuels ... take what we have worked on for the past decade to ... CU-Boulder,s Renewable and Sustainable Energy Institute, or RASEI. "In this project, ...
... Ian Bell, PhD, the Louis Block Distinguished Service Professor ... the Kovler Diabetes Center at the University of Chicago, ... 2012 for his pioneering work in understanding the role ... The prize, the world,s largest award for ...
... scientists produce better climate-resistant corn and other food production plants ... what we eat. Kansas State University geneticists and colleagues ... and prioritize the genes in humans, it improved the likelihood ... control quantitate traits in plants, such as how the plants ...
Cached Biology News:CU-led team receives $9.2 million DOE grant to engineer E. coli into biofuels 2University of Chicago's Graeme Bell receives international diabetes prize 2University of Chicago's Graeme Bell receives international diabetes prize 3Study finds prioritizing rather than canvassing entire plant genome may lead to improved crops 2Study finds prioritizing rather than canvassing entire plant genome may lead to improved crops 3
Other biology definitionOther Tags