View source for Effective Population Size

'''Effective population size''' (''N''<sub>e</sub>) is the size of an idealized population that would experience [[Genetic drift|genetic drift]] at the same rate as the observed population. It is almost always smaller than the census population size, often dramatically so.

A population of 10,000 individuals where only 100 reproduce has an effective size closer to 100 than 10,000. Variance in reproductive success, sex ratio imbalance, and non-random mating all reduce ''N''<sub>e</sub>. The result: drift is stronger than headcounts suggest. For [[Allele Frequency|allele frequency]] changes and [[Neutral Theory of Molecular Evolution|neutral substitutions]], ''N''<sub>e</sub> is the number that matters, not the number you count in a census.

[[Category:Population Genetics]]
[[Category:Evolution]]