X-inactivation - Wikipedia, the free encyclopedia


** X-inactivation **

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The coloration of tortoiseshell and calico cats is a visible manifestation
of X-inactivation. The black and orange alleles of a fur coloration gene
reside on the X chromosome. For any given patch of fur, the inactivation of
an X chromosome that carries one gene results in the fur color of the
other, active gene.
Nucleus of a female cell. Top: Both X-chromosomes are detected, by FISH.
Bottom: The same nucleus stained with a DNA stain (DAPI). The Barr body is
indicated by the arrow, it identifies the inactive X (Xi).
An interphase female human fibroblast cell.^[1] Arrows point to sex
chromatin on DNA (DAPI) in cell nucleus(left), and to the corresponding X
chromatin (right).
Left: DNA (DAPI)-stained nucleus. Arrow indicates the location of Barr
body(Xi). Right: DNA associated histones protein detected
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]

*X-inactivation* (also called *lyonization*) is a process by which one of
the two copies of the X chromosome present in female mammals is
inactivated. The inactive X chromosome is silenced by its being packaged in
such a way that it has 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

Source: en.wikipedia.org/wiki/X-inactivation

does x chromosome inactivation occur in males

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