Evolutionary Genetics: Two-Locus

Try these parameter values:

Selection For the Double-Heterozygote (AAbb)

A: 0.05
a: 0.95
B: 0.95
b: 0.05
wAA: 1.0
wAa: 0.95
waa: 0.9
wBB: 0.8
wBb: 0.9
wbb: 1.0

Evolutionary Genetics: Two-Locus

Selection at multiple loci can have considerably more complicated dynamics than selection at one locus. However, if the loci are independent with regards to selection, then multi-locus genotype frequencies will behave the same as they would in a one-locus system. Two-locus genotype frequencies can be found, for example, by multiplying the corresponding one-locus genotype frequencies.

For example, suppose that f(AA) in the next generation was calculated to be 0.4 and f(Bb) was calculated to be 0.3. Then the frequency of the two-locus genotype, f(AABb) would be 0.4*0.3=0.12.

When the two loci are not independent of each other, complications arise (for example, linkage disequilibrium can result). See the section on linkage equilibrium for more information.

Evolutionary Genetics: Two-Locus

Adjust the initial allelic frequencies and the fitness values to the right:

For best results, begin by setting the fitness values to 1.0, and initial allelic frequencies to 0.5. Then, decrease one or more of the fitness values by a small amount.

The initial allelic and genotypic frequencies are displayed below the graph whereas the run-time frequencies are displayed above the graph.

In this simulaiton, two loci are subjected to independent selection pressures in a population of 5000 individuals. Because the two loci in this simulation are independent with respect to selection gene frequencies at each locus will be identical to the case of one-locus selection.Two-locus genotype frequencies can be found by multiplying the two corresponding one-locus genotype frequencies.