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:4/5/2017)... , April 5, 2017  The Allen Institute for ... Cell Explorer: a one-of-a-kind portal and dynamic digital window ... imaging data, the first application of deep learning to ... stem cell lines and a growing suite of powerful ... for these and future publicly available resources created and ...
(Date:4/4/2017)... YORK , April 4, 2017   EyeLock ... today announced that the United States Patent and Trademark ... patent broadly covers the linking of an iris image ... same transaction) and represents the company,s 45 th ... latest patent is very timely given the multi-modal biometric ...
(Date:3/30/2017)... KONG , March 30, 2017 The ... a system for three-dimensional (3D) fingerprint identification by adopting ground breaking ... into a new realm of speed and accuracy for use in ... at an affordable cost. ... ...
Breaking Biology News(10 mins):
Other biology definition