Pleiotropy occurs when one gene influences multiple, seemingly unrelated phenotypic traits, an example being phenylketonuria, which is a human disease that affects multiple systems but is caused by one gene defect. Andrzej Pękalski, from the University of Wrocław, argues that eugenics can cause harmful loss of genetic diversity if a eugenics program selects a pleiotropic gene that could possibly be associated with a positive trait. Pekalski uses the example of a coercive government eugenics program that prohibits people with myopia from breeding but has the unintended consequence of also selecting against high intelligence since the two go together.