View source for Barr body

A Barr body is an inactivated X [[Chromosome|chromosome]] in a female [[Somatic cells|somatic cell]]. It becomes inactivated by the process of [[Lyonization|lyonization]]; the process is there to ensure only one X chromosome is active. It is initiated from a site called the XIC ([[X inactivation centre|X inactivation centre]])<ref>Augui S, Nora E P, Heard E. Regulation of X-chromosome inactivation by the x-inactivation centre. Nature reviews genetics.2011;12:429-442</ref>. The key products from this site are the non-coding RNA transcripts [[Xist|Xist]] and [[Tsix|Tsix]]. Xist work by coating the X outwards leading to it becoming [[Heterochromatin|heterochromatin]]. Not all genes, however, are silenced and about 10-15% escape inactivation<ref>Alberts B, Johnson A, Lewis J, Raff M, Roberts K and Walter P (2008) Molecular Biology of The Cell, 5th edition, New York: Garland Science</ref>. The equation for calculating Barr bodies is Xn-1, where ‘n’ refers to the number of X chromosomes present on the sex chromosome. For example, Turners Syndrome, XO, results in no Barr bodies whereas people with Klinefelter Syndrome, XXY, have 1 Barr Body. 

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