neutral epistasis opposing epistasis 2013-06-05T20:25:26Z An effect in which individual perturbations of two different genes result in opposite mutant phenotypes (traits measured on the same scale but each on opposing sides relative to the wild type phenotype), and the resulting phenotype of their combination is equal to that of only one of the perturbations. With respect to any single quantifiable phenotype, this may be expressed as an inequality as: (a < wt < b) AND (ab = a OR ab = b) where 'a' and 'b' are the observed phenotype values of the individual perturbations, 'ab' is the observed phenotype value of the double perturbation, and 'wt' is the wild type phenotype value. MI:1276 PSI-MI orchard psi-mi:MI:1285 quantitative epistasis