Final answer:
Lyons's hypothesis for X chromosome inactivation states that in female mammalian embryos, one X chromosome in each cell inactivates by condensing into a Barr body, and the genes on the inactive X chromosome are not expressed. The particular X chromosome that is inactivated in each cell is random, but all cells descended from the inactivated cell will have the same inactive X chromosome.
Step-by-step explanation:
Lyons's hypothesis for X chromosome inactivation states that early in development, when female mammalian embryos consist of just a few thousand cells, one X chromosome in each cell inactivates by condensing into a structure called a Barr body. The genes on the inactive X chromosome are not expressed. The particular X chromosome that is inactivated in each cell is random, but once the inactivation occurs, all cells descended from that cell will have the same inactive X chromosome. By this process, females compensate for their double genetic dose of X chromosome.