Epigenetics generally refers to modifications of the genome that do not involve a change in nucleotide sequence; rather, epigenetic changes involve chemical modifications to the DNA that impact the likelihood that a particular gene will be “turned on or off”. These patterns of activation and inactivation across the genome have been suggested as biological mechanisms that may underlie some forms of gene-environment interplay (El-Sayed et al., 2013). Environmental factors can induce epigenetic changes. In the example likely to be most familiar to readers, maternal licking and grooming of rat pups induces changes in genes related to the stress response (Meaney and Szyf, 2005). In this sense, epigenetic changes can be thought of as one way that environmental experiences get “under the skin” to influence subsequent behavioral outcomes. Epigenetics complements studies of latent and measured G × E—which provide evidence of a statistical interaction—to provide a biologically plausible mechanism for G × E (Tremblay, 2008).
