It has frequently been assumed that the persistence of a deleterious mutation (the average number of generations before its loss) and its pervasiveness (the average number of individuals carrying the gene before its loss) are equal. This is true for a particular simple, widely used infinite model, but this agreement is not general. If hs ≫ 1/(4N_e), where hs is the selective disadvantage of mutant heterozygotes and N_e is the effective population number, the contribution of homozygous mutants can be neglected and the simple approximate formula 1/hs gives the mean pervasiveness. But the expected persistence is usually much smaller, 2(log_e(1/2hs) 1 − γ) where γ = 0.5772. For neutral mutations, the total number of heterozygotes until fixation or loss is often the quantity of interest, and its expected value is 2N_e, with remarkable generality for various population structures. In contrast, the number of generations until fixation or loss, 2(N_e/N)(1 log_e2N), is much smaller than the total number of heterozygotes. In general the number of generations is less than the number of individuals.