One X chromosome is inactivated (Xi) in each cell of a female in order to achieve transcriptional balance. An X linked inactivation centre (Xic) is responsible for the initiation of X inactivation. The exact size of the Xic is unclear but it includes the XIST gene (X-inactivation locus) at Xq13.2. Know more at: http://www.creative-bioarray.com/XIST-Probe-FMDC-54-item-4641.htm