 A very similar effect on the “gene”s eye view’ of selection is caused by additive-by-additive epistasis (Goodnight &amp; Wade 2000; Wade 2001, 2002). The simplest model of this kind of \(\rG \times \rG\), with interaction between loci A and B, each with alternative alleles, results in an average genic selection coefficient acting on the A allele of \(s(p_B - p_b)\), where \(p_B\) and \(p_b\) are the frequencies of alternative alleles at the B-locus that interact in the additive-by-additive model with alleles at the A locus. The relative frequencies of the alternative alleles at the B locus, determine whether the A allele is a “good” gene or a “bad” gene with respect to fitness, a gene of major effect or minor fitness effect, or even a neutral gene when the background alleles are equally abundant (i.e., \(p_B = p_b)\). Whenever allele frequencies of its epistatic partner change, either by drift or selection, the A allele’s selective effect also changes and, like the case of \(\rG \times \rE\), it moves the boundary between the domains of natural selection and random drift  (Fig. 2),  increasing the domain of the latter at the expense of the former.