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.

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
 * $$\Delta q$$ 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, $$pq$$, 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 $$\Delta Q$$ 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 $$\Delta Q$$ 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.