Multi-locus population genetics - Summary
• Population genetics for two or more loci is concerned with changes in the frequencies of haplotypes, which are the multi-locus equivalent of alleles.
• Recombination tends, in the absence of other factors, to make the alleles of different loci appear in random (or independent) proportions in haplotypes. This condition is called linkage equilibrium.
• A deviation from the random combinatorial proportions of haplotypes is called linkage disequilibrium. It can arise because of non-random mating, random sampling, and natural selection.
• For selection to generate linkage disequilibrium, the fitness interactions must be epistatic.
• Pairs of alleles at different loci that co-operate in their effects on fitness are called coadapted. Selection acts to reduce the amount of recombination between coadapted genotypes.
• When selection works on one locus, it will influence gene frequencies at linked loci. The effect is called hitch-hiking.
• Recombination is selectively disadvantageous in so far as it breaks down favorable gene combinations.
• The mean fitness of a population can be drawn graphically for two loci; the graph is called a fitness surface or an adaptive topography.