**The Neutral Equation**

According to the Neutral Theory, observed
**Heterozygosity**
(**H**) (average fraction of heterozygous loci per individual) is a
balance between loss of variation in finite populations of size **N**_{e}
and its replacement by recurrent **mutation** at a rate **u**. Then,
**H = (4N**_{e}u) / (4N_{e}u + 1) : for example, if
N_{e} = 10^{6} and u = 10^{-7}, then
**H** = (0.4)/(0.4 + 1) = **0.29. **As is apparent in the above graph,
which shows he range of observed heterozygosities bracketed in red,
few species approach this value. One interpretation is that
*observed*
population sizes typically overestimates the *effective* population
size.

Text material
© 2005 by Steven M. Carr