Mutations can act to increase diversity, but their rate is only about 10-8 /bp/generation for humans, which is sort of slow. For example, with 3 x 109 base pairs in the genome, this translates to about 30 mutations per genome per generation, or alternatively, 0.01 mutations per 1,000,000 SNPs ( typical public datasets) per generation, or alternatively, only 16 mutations per genome per 40,000 years (assuming 25 years per generation). Clearly, mutations are a weak force and alone can’t counteract the rapid rate at which alleles either become lost or fixed in small drifted populations such as the Onge.
Assuming no selection pressures on an allele, which is usually the case with non-functional intergenic alleles, and genetic drift is the only evolutionary force acting on it, the probability that the allele will eventually become fixed is simply its allele frequency in the population. So for example if allele A has a frequency of 85% within the Onge, then the probability that A will become fixed in due time is 85%, and the probability that A will be lost in due time may be 15%. Generally, my analysis has shown that in small drifted populations, alleles with low frequencies tend to become lost, and alleles with high frequencies tend to become fixed in due time.
According to the Wright–Fisher model, the following formula can be used for approximating the time it takes a neutral allele to become fixed via genetic drift:
T fixed = [ -4Ne (1 – p) ln (1 – p)] / p
where T is the time in generations, p the allele frequency, and Ne the effective breeding population size.
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Originally Posted by arigiery
