创立者效应（英语：founder effect，亦称为创建者效应或创始者效应、始祖效应）是遗传漂变的一种形式，指由带有亲代群体中部分等位基因的少数个体重新创建新的群体，这个群体后来的数量虽然会增加，但因未与其他生物群体交配繁殖，彼此之间基因的差异性甚小。这种情形一般发生于对外隔绝的海岛，或较为封闭的新开辟村落等。

有一个很好的例子可以解释此现象：在委内瑞拉的偏僻山村中，人们患上杭廷顿舞蹈症的几率大大高于外界。因为十九世纪初，一位带有杭廷顿舞蹈症基因的妇女，将自己的基因播撒在个别村民中。其后的历史发展并没有再介入新的基因，遂导致全村的人共享了这一病态基因。

In population genetics, the founder effect is the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population. It was first fully outlined by Ernst Mayr in 1942, using existing theoretical work by those such as Sewall Wright. As a result of the loss of genetic variation, the new population may be distinctively different, both genotypically and phenotypically, from the parent population from which it is derived. In extreme cases, the founder effect is thought to lead to the speciation and subsequent evolution of new species.