Epigenetics is an emerging scientific field. Research focuses on the chemical changes that affect gene expression but do not alter the base sequence of DNA. These chemical changes include methylation, the addition of a methyl group to certain nitrogen bases. Researchers are studying these patterns of gene expression, which are passed on from parent to offspring. They are also studying how environmental factors can change the way in which genes are expressed. A growing body of evidence suggests that a wide variety of illnesses and behaviors may be linked to epigenetic mechanisms. These include various cancers, cognitive dysfunction, and autoimmune diseases. The environmental factors suspected of altering epigenetic processes include heavy metals, pesticides, tobacco smoke, and radioactivity.