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:7/22/2014)... A probiotic that prevents obesity could be on ... in the gut inhibit weight gain, insulin resistance ... in mice, Vanderbilt University investigators have discovered., "Of ... human," said senior investigator Sean Davies, Ph.D., assistant ... of the negative consequences of obesity in mice, ...
(Date:7/22/2014)... New Rochelle, NY -- Stem cells offer much promise ... transplantation approaches stem cell survival is poor, limiting their ... improve the survival and optimize their therapeutic function after ... BioResearch Open Access , a peer-reviewed journal from Mary ... on the BioResearch Open Access website ...
(Date:7/22/2014)... Curtin University-led research has shown squirrels have adapted to ... just as well, if not better, than their fellow ... Lecturer at Curtin,s Department of Environment & Agriculture, led ... to modify their behaviour in urban environments and prevent ... such as staying on the footpath. , "As ...
Breaking Biology News(10 mins):Vanderbilt study shows therapeutic bacteria prevent obesity in mice 2New York squirrels are nuts about city life 2
... Using satellite data, scientists have produced a first-of-its kind map ... are other local- and regional-scale forest canopy maps, the new ... on one uniform method. The map, based on data ... scientists build an inventory of how much carbon the world,s ...
... Spanish . Two good tips for preventing ... troughs and add chlorine to the water. That,s according ... the agency,s Animal Waste Management Research Unit in Bowling Green, ... a hydrologist at Bowling Green, and other colleagues. Stainless ...
... in French . Men who had a history ... cancer, according to a study carried out by researchers at INRSInstitut ... Montral, and McGill University. The findings, published in the Annals ... had a lower risk of lung cancer while those with a ...
Cached Biology News:First-of-its-kind map details the height of the globe's forests 2Dairy farmers can fight growing disease threat with chlorine and stainless steel 2Asthma and eczema sufferers have a lower risk of developing a cancer 2
Other biology definitionOther Tags