title: Association mapping reveals the role of purifying selection in the maintenance of genomic variation in gene expression.
abstract: The evolutionary forces that maintain genetic variation in quantitative traits within populations remain poorly understood. One hypothesis suggests that variation is under purifying selection, resulting in an excess of low-frequency variants and a negative correlation between minor allele frequency and selection coefficients. Here, we test these predictions using the genetic loci associated with total expression variation (eQTLs) and allele-specific expression variation (aseQTLs) mapped within a single population of the plant Capsella grandiflora. In addition to finding eQTLs and aseQTLs for a large fraction of genes, we show that alleles at these loci are rarer than expected and exhibit a negative correlation between phenotypic effect size and frequency. Overall, our results show that the distribution of frequencies and effect sizes of the loci responsible for local expression variation within a single outcrossing population are consistent with the effects of purifying selection.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, Toronto ON, Canada M5S 3B2 em.josephs@utoronto.ca.
authors.forename: Emily B
authors.initials: EB
authors.lastname: Josephs
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, Toronto ON, Canada M5S 3B2.
authors.forename: Young Wha
authors.initials: YW
authors.lastname: Lee
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, Toronto ON, Canada M5S 3B2.
authors.forename: John R
authors.initials: JR
authors.lastname: Stinchcombe
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, Toronto ON, Canada M5S 3B2.
authors.forename: Stephen I
authors.initials: SI
authors.lastname: Wright
mesh_terms: D000483:Alleles; D001482:Base Composition / Q000235:genetics; D029687:Capsella / Q000235:genetics*; D002874:Chromosome Mapping; D018506:Gene Expression Regulation, Plant; D005787:Gene Frequency / Q000235:genetics; D017343:Genes, Plant; D014644:Genetic Variation; D018745:Genome, Plant; D015810:Linkage Disequilibrium / Q000235:genetics; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D040641:Quantitative Trait Loci / Q000235:genetics; D011995:Recombination, Genetic / Q000235:genetics; D012641:Selection, Genetic
keywords: association mapping; gene expression; population genomics