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Tsix is a non-coding RNA gene that is anti-sense to the Xist strand. This is an important component within mammals as the male and females have different gametes, and more importantly different number of X chromosomes.

Tsix is derived from the reverse of Xist, which stands for X-inactive specific transcript[1]. Since the females have double the amount of X's, it leads to dosage compensation problems as double the number of genes are expressed. This is avoided by the Tsix binding to the Xist and being expressed. This expression of Tsix causes the inactivation of the extra X chromosome within the females. Furthermore, Tsix, since many Xist binds on to the X chromosome that becomes inactivated, also prevents the accumulation of Xist on the active X chromosome to maintain its euchromatin state in the future[2].


  1. Lee JT, Davidow LS, Warshawsky D (1999). "Tsix, a gene antisense to Xist at the X-inactivation centre". Nat. Genet. 21 (4): 400–4. doi:10.1038/7734. PMID 10192391.
  2. Bacher, C. P., Guggiari, M., Brors, B., Augui, S., Clerc, P., Avner, P., Eils, R., Heard, E. Transient colocalization of X-inactivation centres accompanies the initiation of the X inactivation. Nature Cell Biol. 8: 293-299, 2006. [PubMed: 16434960, related citations]
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