Final answer:
In females, one of the two X chromosomes is inactivated during embryonic development through a process called X inactivation. The XIST RNA produced by the Xist gene on the inactive X chromosome helps establish and maintain its inactive state.
Step-by-step explanation:
In females, one of the two X chromosomes is inactivated during embryonic development due to epigenetic changes to the chromatin. This process is called X inactivation. The inactive X chromosome condenses into a structure called a Barr body. The Xist (X-inactive specific transcript) gene on the inactive X chromosome produces the XIST RNA, which coats the inactive X chromosome and helps to establish its inactive state. The XIST RNA acts as a scaffold for recruiting various proteins that contribute to the inactivation of the X chromosome.