pleiotropy /plaɪˈɒtɹəpi/ noun2 •The influence of a single gene on multiple phenotypic traits; pleiotropism.This experimental design is analogous to the experiment that we performed to test whether antagonistic pleiotropy operates as a genetic mechanism in the evolution of late-life mortality rate plateaus. — 2011 •The existence of drug effects (especially beneficial effects) other than the one for which the drug was designed. formspleiotropies