page_title: X-inactivation
hierarchical_section_title: X-inactivation
caption_attribution_description: English: The figure shows confocal images from a combined RNA-DNA FISH experiment for Xist in female mouse fibroblast cells (Female-biased expression of long non-coding RNAs in domains that escape X-inactivation in mouse, B Reinius et al 2010, BMC Genomics (6), http://www.biomedcentral.com/1471-2164/11/614/abstract). The figure was adapted from Figure 5 in the original publication and contrast was adjusted to make the figure clear in thumbnail format. Open access: Unrestricted use, distribution and reproduction in any medium is permitted, provided the original article is properly cited.
context_page_description: X-inactivation is a process by which one of the copies of the X chromosome is inactivated in therian female mammals. The inactive X chromosome is silenced by it being packaged into a transcriptionally inactive structure called heterochromatin. As nearly all female mammals have two X chromosomes, X-inactivation prevents them from having twice as many X chromosome gene products as males, who only possess a single copy of the X chromosome.
  The choice of which X chromosome will be inactivated is random in placental mammals such as humans, but once an X chromosome is inactivated it will remain inactive throughout the lifetime of the cell and its descendants in the organism. Unlike the random X-inactivation in placental mammals, inactivation in marsupials applies exclusively to the paternally-derived X chromosome.
context_section_description: X-inactivation (also called lyonization, after English geneticist Mary Lyon) is a process by which one of the copies of the X chromosome is inactivated in therian female mammals. The inactive X chromosome is silenced by it being packaged into a transcriptionally inactive structure called heterochromatin. As nearly all female mammals have two X chromosomes, X-inactivation prevents them from having twice as many X chromosome gene products as males, who only possess a single copy of the X chromosome (see dosage compensation).
  The choice of which X chromosome will be inactivated is random in placental mammals such as humans, but once an X chromosome is inactivated it will remain inactive throughout the lifetime of the cell and its descendants in the organism. Unlike the random X-inactivation in placental mammals, inactivation in marsupials applies exclusively to the paternally-derived X chromosome.
caption: The figure shows confocal microscopy images from a combined RNA-DNA FISH experiment for Xist in fibroblast cells from adult female mouse, demonstrating that Xist RNA is coating only one of the X-chromosomes. RNA FISH signals from Xist RNA are shown in red color, marking the inactive X-chromosome (Xi). DNA FISH signals from Xist loci are shown in yellow color, marking both active and inactive X-chromosomes (Xa, Xi). The nucleus (DAPI-stained) is shown in blue color. The figure is adapted from:.[2]
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