Question

Explain why the rate at which allele frequencies change under drift is influenced by the effective population size, yet the neutral substitution rate under drift is uncorrelated with population size.

Answer 1

we replace the census population size Nc by an effective population size Ne . Ne then reflects the size of an ideal population that experiences genetic drift at the rate of the population i. Hence, if we are able to transform Nc to Ne in some meaningful way, we can still quantify the rate at which genetic diversity gets lost through genetic drift using the same mathematical model. It is important to note that we need some read out to measure the effects of genetic drift and calibrate the effective population size accordingly. This can be the loss of heterozygosity in a population, the degree of inbreeding, genetic variance, the efficiency of selection, or the rate of coalescence. Accordingly, the effective population size is defined by the quantity of interest as e.g. the inbreeding effective size, the coalescence effective size, etc.