(105). This implies the presence of a gene-environment interaction, such that certain environments allow for greater expression of genetic effects, possibly due to the availability of opportunities for individuals to show their genetic predispositions (6). While twin studies of gene-environment interaction have been useful in explaining how the effect of genes may change as a function of the environment, molecular genetic studies of gene-environment interaction have been useful in parsing out the role of specific genes influencing cigarette use behaviors through the testing of the main effect of a specific gene of interest from candidate and genome wide association studies on a given cigarette use phenotype and the testing of interactions between the specific genes of interest and the environment.
