Animation of epigenetic modification of DNA. Epigenetics is the study of the heritable changes in gene expression caused by factors other than a change in the DNA sequence itself. Genes can be turned on or off by a variety of factors, including environmental factors, which can then be passed on through the normal replication of the modified genome during cell division. The most common chemical means of switching a gene off is to methylate it, attaching a methyl group to the gene磗 DNA. This is represented by the glowing spheres on the DNA molecule.