Final answer:
The long noncoding RNA Xist silences genes on the X chromosome by methylation of DNA and hypo-acetylation of histones, causing nucleosomes to pack tightly together. This inactivates one of the X chromosomes. The process involves the Xist gene product and the lncRNA XistAR.
Step-by-step explanation:
The long noncoding RNA Xist silences genes on the X chromosome by methylation of DNA and hypo-acetylation of histones, which causes the nucleosomes to pack tightly together, inactivating one of the X chromosomes. Barr bodies form in human females when one of the X chromosomes in somatic cells is inactivated, and this process involves the Xist gene product and the recently discovered lncRNA XistAR. These epigenetic changes to the chromatin result in the silencing of genes on the inactivated X chromosome.