Biology:General selection model

Short description: Model of population genetics

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.

Equation

The General Selection Model applied to a single gene with two alleles (let's call them A1 and A2) is encapsulated by the equation:

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

where:

[math]\displaystyle{ p }[/math] is the frequency of allele A1

[math]\displaystyle{ q }[/math] is the frequency of allele A2

[math]\displaystyle{ \Delta q }[/math] is the rate of evolutionary change of the frequency of allele A2

[math]\displaystyle{ W_0,W_1, W_2 }[/math] are the relative fitnesses of homozygous A1, heterozygous (A1A2), and homozygous A2 genotypes respectively.

[math]\displaystyle{ \overline{W} }[/math] is the mean population relative fitness.

In words:

The product of the relative frequencies, [math]\displaystyle{ pq }[/math], is a measure of the genetic variance. The quantity pq is maximized when there is an equal frequency of each gene, when [math]\displaystyle{ p=q }[/math]. In the GSM, the rate of change [math]\displaystyle{ \Delta Q }[/math] is proportional to the genetic variation.

The mean population fitness [math]\displaystyle{ \overline{W} }[/math] is a measure of the overall fitness of the population. In the GSM, the rate of change [math]\displaystyle{ \Delta Q }[/math] is inversely proportional to the mean fitness [math]\displaystyle{ \overline{W} }[/math]—i.e. when the population is maximally fit, no further change can occur.

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

See also

• Darwinian fitness
• Hardy–Weinberg principle
• Population genetics