polygenic adaptation - senecio7の日記

Pritchard JK & Di Rienzo A 2010 Adaptation — not by sweeps alone. Nat Rev Genet 11:665-667.

within the population genetics community, adaptation is typically viewed as involving selective sweeps that drive beneficial alleles from low to high frequency in a population
this view of adaptation that proceeds by selective sweeps at key loci is too limited
classical selection models of artificial and natural selection in the quantitative genetics literature emphasize the importance of modest changes in allele frequencies at many loci
that is, 'polygenic adaptation'
polygenic models have received too little attention in the population genetics community

many — possibly even most — adaptive events in natural populations occur by polygenic adaptation
polygenic adaptation could allow rapid adaptive shifts
yet would often go undetected using conventional methods for detecting selection
polygenic adaptation is qualitatively different from the models of adaptive substitutions that dominate the population genetics literature

if there is already considerable heritable variation underlying the phenotype in question, then the population can adapt rapidly to the new conditions at a speed that depends on the strength of selection and the heritability of the trait
the key point is that we should expect such an adaptation to occur by small allele frequency shifts spread across many loci
strong selection for increased height could be very effective, as height is extremely heritable
at the level of individual SNPs, the effect of selection would be rather weak, exerting just a small upward pressure in favour of each of hundreds of 'tall' alleles
suppose that at 500 SNPs, the tall alleles each increase the expected height of a person by 2 mm
an average shift of just 10% in the population allele frequency of each tall allele would increase average height in the population by 20 cm (assuming that SNPs contribute additively)
a dramatic adaptive response could result from modest allele frequency changes at many loci
adaptation could occur without dramatic allele frequency changes
without adaptive fixation events

on the theoretical side, there is a need to bridge the gap between the classical quantitative perspective and the population genetics approach (which has focused more explicitly on quantities that can be measured in molecular data)

the effect of this mode of adaptation on substitution rates would likely be modest
as the tall alleles would include a mixture of ancestral and derived alleles