The field of environmental genetics can be viewed from three perspectives: the ways that the environment affects gene expression, how the environment changes the individual genome, and how specific environment factors bring about gene frequency changes.

There are numerous ways that gene expression is affected by environmental conditions. Certain factors in the external or internal environment of an organism will, in effect, turn on or induce the reading of certain genes. Possibly the best known of these is the lac operon model of Jacob and Monod.

A well-known general type of environmental induction can occur through chemicals that cause cancers and other abnormal growths. While some carcinogens cause cancer through actual change in genetic structure others cause tumors. Diethylstilbestrol (or DES) acts as an estrogen and is a potent cause of tumors. DES was used to help women conceive in the mid-twentieth...