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.
