Simulated population fitness under different levels of pleiotropy, i.e. the number of phenotypes controlled by a single QTL (horizontal axis).

Phenotypes start from an initial value 0 and selection acts to move them towards three different optima. Shown are medians and interquartile ranges (IQR) from 300 simulation. The fitness estimates were normalized in relation to the non-pleiotropic class (median = 0, IQR = 1).