additive genetic interaction defined by inequality true additive genetic interaction (sensu inequality) Single-mutant phenotype effects combine to give a double-mutant effect different from the wild type and different from single mutant effect. For instance, WT < a = b < ab, b < WT = ab < a, WT < a < b < ab, b < WT < ab < a, and all additional inequalities obtained by interchanging a and b, or reversing the effect of both a and b. PSI-MI MI:0799 additive