Effect of temporal fluctuation of selection coefficient on gene frequency in a population.

The diffusion equations describing the change of gene frequencies are extended to indlude the effect of temporal fluctuation of selection coefficient that may persist for some generations. The equilibrium distribution of gene frequencies and the fixation probability of a mutant gene are obtained from the extended equations. Comparison is made with the experimental data on protein polymorphism. A possible bearing of the fluctuation of selection coefficient on the problem of molecular evolution is discussed in relation to the neutral theory.