Polygenic dynamics underlying the response of quantitative traits to directional selection

Area of Science:

• Evolutionary genetics
• Population genetics
• Quantitative genetics

Background:

• Directional selection drives adaptive evolution.
• Understanding genetic and phenotypic responses is crucial.
• Finite population size and mutation dynamics complicate predictions.

Purpose of the Study:

• To model the response of a quantitative trait to exponential directional selection in finite haploid populations.
• To analyze both genetic and phenotypic changes over time.
• To provide accurate approximations for evolutionary dynamics.

Main Methods:

• Utilized an infinite sites model with additive mutation effects.
• Employed a supercritical Galton-Watson process for initial dynamics.
• Derived approximations for mutant frequency in Wright-Fisher populations.
• Validated with comprehensive simulations.

Main Results:

• Mutant copy-number distribution accurately reflects deterministic increase.
• Approximations for trait mean, variance, and segregating sites are highly accurate, even in quasi-stationary phases.
• Mutation rate (Θ) determines adaptation patterns (few loci vs. many).
• Selection strength primarily influences the rate of adaptation.

Conclusions:

• The model accurately predicts trait evolution under directional selection.
• Refined classical results on adaptation dynamics.
• Highlights the distinct roles of mutation rate and selection strength in shaping evolutionary trajectories.