The General Selection Model (GSM) is a model of population genetics that describes how a population's allele frequencies will change when acted upon by natural selection.
The General Selection Model applied to a single gene with two alleles (let's call them A1 and A2) is encapsulated by the equation:
Δ q = p q [ q ( W 2 − W 1 ) + p ( W 1 − W 0 ) ] W ¯
where:
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 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 W ¯ —i.e. when the population is maximally fit, no further change can occur.
The remainder of the equation, [ q ( W 2 − W 1 ) + p ( W 1 − W 0 ) ] , refers to the mean effect of an allele substitution. In essence, this term quantifies what effect genetic changes will have on fitness.
