General selection model

The General Selection Model (GSM) is a model of population genetics that describes how a population's genotype will change when acted upon by natural selection.

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Equation

The General Selection Model is encapsulated by the equation:

$\Delta q=\frac{pq \big[q(W_2-W_1) + p(W_1 - W_0)\big ]}{\overline{W}}$

where:

p

is the frequency of the dominant gene

q

is the frequency of the recessive gene

Δ q

is the rate of evolutionary change of the frequency of the recessive gene

W 0, W 1, W 2

are the relative fitnesses of homozygous dominant, heterozygous, and homozygous recessive genotypes respectively.

$\overline{W}$ is the mean population relative fitness.

In words:

The product of the relative frequencies, $p q$ , is a measure of the genetic variance. The quantity pq is maximized when there is an equal frequency of each gene, when $p = q$ . In the GSM, the rate of change $Δ Q$ is proportional to the genetic variation.

The mean population fitness $\overline{W}$ is a measure of the overall fitness of the population. In the GSM, the rate of change $Δ Q$ is inversely proportional to the mean fitness $\overline{W}$ -- i.e. when the population is maximally fit, no further change can occur.

The remainder of the equation, $\big[q(W_2-W_1) + p(W_1 - W_0)\big ]$ , refers to the mean effect of an allele substitution. In essence, this term quantifies what effect genetic changes will have on fitness.