The Genome-Wide Effect of Drift and Selection over a Single Generation
The relative importance of genetic drift versus selection to evolutionary change has long been debated. This debate has mainly focused over long-time-scales (e.g. hundreds of thousands of generations), leaving the question of short-term evolutionary change relatively unaddressed. Our knowledge about the effects of selection on genetic change over short time scales is often based on identifying…
For centuries, scholars have contended over the relative significance of genetic drift versus selection in the course of evolution. This discourse has predominantly centered on prolonged periods, leaving the nuances of short-term evolutionary changes largely unexplored. Our understanding of how selection influences genetic alterations over brief periods is often derived from identifying pronounced shifts in allele frequencies at a select few loci exhibiting substantial selective advantages.
However, selection frequently impacts polygenic traits, wherein the minor fluctuations in allele frequencies at numerous loci, which may blend with genetic drift, govern the short-term response.
In this study, we endeavor to measure the comprehensive impact of polygenic selection on a single generation, employing the premise that alleles exhibiting stronger genetic correlations (LD) with selected alleles are anticipated to exhibit larger variations in allele frequency change than predicted by genetic drift alone. We establish mathematical formulations linking the variability in LD among loci to the variance in allele frequency change attributable to linked selection and genetic drift, subsequently utilizing this theoretical framework to quantify the role of linked selection in a single generation's allele frequency shift.
To validate our methodology, we dissect the genome-wide allele frequency variation in the UK Biobank, utilizing fitness proxy phenotypes as our basis. Our findings reveal that selection, though minor, does exert a discernible influence, with genetic drift accounting for the overwhelming majority of the allele frequency fluctuations.
This analytical framework has the potential to be applied to other organisms where data exist on the number of offspring or allele frequencies across successive generations. This would facilitate the investigation of the short-term, genome-wide ramifications of polygenic selection across a diverse spectrum of species.
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