text: One way this happens is by epigenetic silencing/chromatin remodeling. Your DNA (which contains your genes) is wrapped around proteins called histones that help to organize your DNA and keep it from getting all tangled up. Histones can be acetylated and deacetylated by proteins called HATs and HDACs. These proteins change how tightly or loosely your DNA is wrapped up. When the DNA is more loose the genes can be expressed, but the ones you don't need in adult cells can be very tightly wrapped. A similar thing happens to half of the X-chromosomes in women. In each cell, women express genes off of one or the other of their X-chromosomes, but the other ones becomes tightly wrapped into a structure called a Barr body.