Definitions

Epistasis

the interaction of non-allelic genes in which one gene (epistatic gene) masks the expression of another at a different locus. Lincoln, R. Boxshall, G. and Clark, P. 1998 A Dictionary of Ecology, Evolution, and Systematics 2nd ed. (Cambridge Univ. Press) p. 104. Also, in quantitative genetics, epistasis generally refers to situations where genetic factors (loci) show evidence of non-additive effects on the phenotype. Phillips, P.C. 1998 The language of gene interaction. Genetics 149:1167-1171.

Pleiotropic

used of a gene [or mutation] that has more than one, apparently independent, phenotypic effect. Lincoln, R. Boxshall, G. and Clark, P. 1998 A Dictionary of Ecology, Evolution, and Systematics 2nd ed. (Cambridge Univ. Press) p. 235.

Genotype by environment interaction

a situation in which identical genotypes perform differently (i.e. have different phenotypes) in different environments.

Developmental constraint

Refers to situations where the developmental program may limit the possibilities for phenotypic evolution of a species.

Historical contingency

Refers to situations where evolutionary change in a species may be limited by factors such as the amount and type of genetic variation present in its ancestral population(s), the biogeographical history of the species, and its ancestral interactions with other species and the environment.