A Barr body is an inactivated X chromosome in a female somatic cell. It becomes inactivated by the process of lyonization; the process is there to insure only one X chromosome is active. It is initiated from a site called the XIC (X inactivation centre)
. The key products from this site are the non-coding RNA transcripts Xist and Tsix. Xist work by coating the X outwards leading to it becoming heterochromatin. Not all genes however are silenced and about 10-15% escape inactivation.
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