Barr body
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 ensure only one X chromosome is active. It is initiated from a site called the XIC (X inactivation centre)[1]. 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[2]. The equation for calculating barr bodies is Xn-1,n refers to the number of X chromosomes present on the sex chromosome.