Neutral
        Equation for 3 uNe vs He
        cropped

The Neutral Equation

    According to the Neutral Theory, in the absence of natural selection (s = 0), expected heterozygosity (He) in a finite population of effective size Ne is a balance between loss of variation by genetic drift  and its replacement by recurrent mutation at a rate µ. Then it can be shown,

He = (4Neµ) / (4Neµ + 1)

     If Ne = 106 and µ = 10-6, then Neµ = 1 and expected He = (4)/(4 + 1) = 0.80. However, the observed range 0.001 < Hobs < 0.25 over a wide range of species is much smaller than this expected value. One interpretation is that the effective population size (Ne) for most species is much smaller than the observed population count (Nc). Thus, if Ne = 104, then Neu = 0.001 and He = (0.004)/(0.004 + 1) = (0.004)/(1) = 0.04, a fairly typical value.

    A modified form is the Nearly-Neutral Theory where 0 ~ s << 1, which would allow larger populations to have lower
He.


Text material © 2021 by Steven M. Carr