The effect of directional and heterotic selection on the standardized variance of gene frequency .**GRAPHIC**. was examined. Heterotic selection always results in f values lower than those expected due to drift alone. Additive directional selection can result in low of values, but values larger than those expected due to drift will be observed under additive selection with low initial gene frequency, or when the populations are separated for a very long period of time in which case f expected due to drift is quite high (around 0.7 or greater). The effect of selection on f is unlikely to be detected if the observed value of f is less than 0.1.