Abstract
Deleterious alleles are introduced into the population by mutation, and then change in frequency as a result of the combined effects of genetic drift and natural selection. Unless the allele confers an advantage in certain environments, the frequency at which it will be found in a population reflects a balance between the rate at which it is introduced by mutation and the rate at which it is eliminated by purifying selection, modulated by the effects of genetic drift. This phenomenon is known as " mutation-selection-drift equilibrium ". This lecture looks at the model that describes this equilibrium, and at studies that apply it to better understand the persistence of disease-associated alleles in human populations.
