Animation of epigenetic tagging of DNA. The DNA molecule is seen coiling around histone proteins red, then coiling again to form a densely_packed chromatin strand. A green light represents reading of the structure, which then reconforms itself into an even more tightly_packed form. This new form is so tightly packed that the genes on the DNA within it are inactivated for subsequent readings. Chemically this is typically accomplished by the deacetylation of the histone proteins. This turns off the affected gene. This is a heritable change in the DNA, one that can be transmitted to daughter cells during replication. The study of the heritable modification of gene expression is known as epigenetics.