Random events in population genetics
The genotypes at a locus may all have the same fitness. Then, in small populations, gene frequencies evolve by random genetic drift. This tutorial explains what it means and why it happens. We then see how drift can ultimately fix one allele, and in a sense undermine the Hardy-Weinberg equilibrium. Finally, we add the effects of mutation, which introduces new variation: the variation observed in a population will be a balance between the drift to homozygosity and mutation that creates heterozygosity.