Final answer:
X inactivation in females is a process that randomly inactivates one of the two X chromosomes in each cell. The inactivation leads to the formation of a Barr body, preventing the genes on the inactive X chromosome from being expressed. The Xi produced ncRNA acts on the inactivated X chromosome, not the active one.
Step-by-step explanation:
X inactivation is a process that occurs in females during embryonic development, in which one of the two X chromosomes is randomly inactivated in each cell. This inactivation leads to the formation of a Barr body, a condensed structure that prevents the genes on the inactive X chromosome from being expressed.
The XistAR ncRNA is involved in this process, along with the Xist gene product, by recruiting other proteins and inducing epigenetic changes to the chromatin.
The reason the Xi produced ncRNA does not act on the "other" X chromosome is because X inactivation ensures that only one X chromosome is active per cell. Once an X chromosome is inactivated, all the cells derived from it will have the same inactive X chromosome. This inactivation is necessary to balance the double genetic dose of X chromosome in females and prevent overexpression of X-linked genes.