nonadditive
adjective
non·ad·di·tive ˌnän-ˈa-də-tiv 
1
: not having a numerical value equal to the sum of values for the component parts
2
: of, relating to, or being a genetic effect that is not additive
nonadditive effects of epistasis
nonadditivity
ˌnän-ˌa-də-ˈti-və-tē
noun 
Word History
First Known Use
1907, in the meaning defined at sense 1
Medical Definition
nonadditive
adjective
non·ad·di·tive (ˈ)nän-ˈad-ət-iv
: of, relating to, or being a genetic effect that is not additive