The consideration of variability can also be extended to provide an explanation for why GxE effects might be observed in one racial/ethnic group but not another. Social control and social trigger mechanisms, according to Dick and Kendler10 and Boardman et al.8, predict reduced genetic influences under low-risk environmental conditions and, conversely, increased genetic influences under more adverse conditions (illustrated in Figure 2, top panel). GxE effects are more likely observed in population groups when members are represented along the continuum of low- to high-risk environments, and less likely when members are overly represented at any single point along the continuum, whether more low-risk or adverse (illustrated in Figure 2, bottom left and right panels, respectively). Alike, selected genetic marker(s) must vary in the targeted population, with GxE effects being more likely observed when, in the case of biallelic markers, the frequencies of the common and minor alleles are more balanced. See Duncan and Keller6 for a more detailed illustration of the relationships between sample size, variance, and statistical power to detect GxE effects.
