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Equation 2 · Part 3 · From Origins to Frontier: A History of Evolutionary Biology and Ecology

Symbol N_e

Var⁡(Δp)=p(1−p)2Ne,\operatorname{Var}(\Delta p) = \frac{p(1-p)}{2N_e},
NeN_e

What this part means

NeN_e occurs below the fraction bar. The quantity above the bar is divided by this expression; zero is excluded as a denominator.

Its job in the formula

NeN_e occurs below the fraction bar. The quantity above the bar is divided by this expression; zero is excluded as a denominator.

The passage around this formula

…lacked: a formal account of genetic drift, the random change in allele frequency from generation to generation caused by finite population size [ 3 ] . Wright showed that in a randomly mating population of effective size NeN_e , the variance in allele frequency change per generation from sampling alone is Var⁡(Δp)=p(1−p)2Ne\operatorname{Var}(\Delta p) = \frac{p(1-p)}{2N_e}. for a diploid population starting at allele frequency p . This single expression carries a real consequence: small populations can fix or lose alleles by chance alone, independent of whether…

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