The effect of gene interactions on the long-term response to selection
The role of gene interactions in the evolutionary process has long
been controversial. Although some argue that they are not of
importance, because most variation is additive, others claim that
their effect in the long term can be substantial. Here, we focus on
the long-term effects of genetic interactions under directional
selection assuming no mutation or dominance, and that epistasis is
symmetrical overall. We ask by how much the mean of a complex
trait can be increased by selection and analyze two extreme
regimes, in which either drift or selection dominate the dynamics
of allele frequencies. In both scenarios, epistatic interactions affect
the long-term response to selection by modulating the additive
genetic variance. When drift dominates, we extend Robertson
’
s
[Robertson A (1960)
Proc R Soc Lond B Biol Sci
153(951):234
−
249]
argument to show that, for any form of epistasis, the total response
of a haploid population is proportional to the initial total genotypic
variance. In contrast, the total response of a diploid population is
increased by epistasis, for a given initial genotypic variance. When
selection dominates, we show that the total selection response can
only be increased by epistasis when s
ome initially deleterious alleles
become favored as the genetic background changes. We find a sim-
ple approximation for this effect and show that, in this regime, it is
the structure of the genotype - phenotype map that matters and not
the variance components of the population.
113
16
4422 - 4427
4422 - 4427
National Academy of Sciences
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