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## Variance of allele frequencies between generations

For a binomial distribution

Applying this to our situation,

Var measures the amount of uncertainty about allele frequencies in the next generation, given the current allele frequency. As you probably guessed long ago, the amount of uncertainty is inversely proportional to population size. The larger the population, the smaller the uncertainty.

If you think about this a bit, you might expect that a smaller variance would slow down'' the process of genetic drift--and you'd be right. It takes some pretty advanced mathematics to say how much the process slows down as a function of population size,10 but we can summarize the result in the following equation:

where is the average time to fixation of one allele or the other and is the current allele frequency.11So the average time to fixation of one allele or the other increases approximately linearly with increases in the population size.

Next: Analogy to inbreeding Up: General properties of genetic Previous: General properties of genetic
Kent Holsinger 2012-09-23