The cells of female mammals have a dosage problem, because they have twice as many X chromosomes as are needed in the body. Consequently, one of them is randomly selected and switched off already during early embryonic development. The Xist gene awakens and produces hundreds of RNA molecules, encasing one X chromosome and making it shrink into a small lump.
Click here for original story, New research sheds light on the division of labor among genetic switches
Source: Phys.org