A related issue concerns the choice of the genetic model in G×E research. The bi-allelic nature of a genetic locus necessitates a choice between three genetic models (additive, recessive, and dominant). Exact replication would require that the same genetic model is detected across different studies. This requirement may be sensible if studies use the same measures (i.e., the phenotype and environmental exposures are ascertained in the same way). In the present study, we measured depression in the same way across the two cohorts but had to rely on different measures of maltreatment in these cohorts. Exposure measurement heterogeneity has implications for matching the genetic model across studies, because the “correct” genetic model could vary depending on the environmental exposure (Uher and McGuffin, 2008). Although the present results favor the hypothesis that the 5-HTTLPR short allele confers risk against a background of childhood maltreatment, we cannot establish whether the genetic effect is additive, recessive, or dominant. Across the two cohorts, we found support for recessive effects, additive effects, and to a lesser extent dominant effects. The literature about the interaction between
