基因多效性（pleiotropy）一个基因可以影响与其无关的性状特征的现象，简单地说就是可以由一个基因影响多个蛋白质的表达。

例如：血红蛋白H病是由于一个控制血红蛋白ɑ链合成合成的调控基因发生了突变，不仅引起贫血症状，还可以在胚胎期影响患儿面部的形态发育。

Pleiotropy occurs when one gene influences two or more seemingly unrelated phenotypic traits. Consequently, a mutation in a pleiotropic gene may have an effect on some or all traits simultaneously. An example is phenylketonuria, a human disease that affects multiple systems but is caused by one gene defect. Pleiotropic gene action can limit the rate of multivariate evolution when natural selection, sexual selection or artificial selection on one trait favours one specific version of the gene (allele), while selection on other traits favors a different allele. The underlying mechanism of pleiotropy in most cases is the effect of a gene on metabolic pathways that contribute to different phenotypes. Genetic correlations and hence correlated responses to selection most often exemplify pleiotropy.