Modeling of genotype by environment interactions. Trait values (y axis) are presented in two environments, E1 and E2. A) The value of an individual phenotype is given with respect to the presence (1) or absence (0) of an SNP (S); rσg is the effect of the SNP in E1; (1 + λ) rσg is the effect of the SNP in E2. The coefficient λ is a numerical value that quantifies the change in the SNP effect from one environment to another. B) A marker correlated with population background is included, in addition to the S marker. The variable Bk denotes the presence (1) or absence (0) of this marker. The SNP effect (rσg) remained stable from environment E1 to E2 when Bk was absent. The size of this SNP effect varied with environment only in the presence of Bk.