obsolete neutral epistasis true 2013-06-05T20:22:53Z orchard MI:1275 PSI-MI OBSOLETE: An effect in which individual perturbations of two different genes result in different mutant phenotypes (which are EITHER traits measured on the same quantitative scale but each significantly deviating, in opposite directions, from wild type, OR completely (qualitatively) different phenotypes), 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) OR (a != wt AND b != wt AND a != 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, 'wt' is the wild type phenotype value, and 'a != b' indicates qualitatively different phenotypes.