X chromosome
In human cells with more than one X chromosome, two long non-coding RNAs are produced: Tsix is produced by one X chromosome, and Xist is produced by all of the other X chromosomes. Tsix is a long non-coding RNA that prevents repression of an X chromosome, while Xist is a long non-coding RNA that acts to repress and condense an entire X chromosome. The actions of Xist serve to create a Barr body in the cell.