Monnahan, Patrick JosephKelly, John K.2015-06-152015-06-152015-05-11Monnahan PJ, Kelly JK (2015) Epistasis Is a Major Determinant of the Additive Genetic Variance in Mimulus guttatus. PLoS Genet 11(5): e1005201. http://dx.doi.org/10.1371/journal.pgen.1005201https://hdl.handle.net/1808/18068A grant from the One-University Open Access Fund at the University of Kansas was used to defray the author’s publication fees in this Open Access journal. The Open Access Fund, administered by librarians from the KU, KU Law, and KUMC libraries, is made possible by contributions from the offices of KU Provost, KU Vice Chancellor for Research & Graduate Studies, and KUMC Vice Chancellor for Research. For more information about the Open Access Fund, please see http://library.kumc.edu/authors-fund.xml.The influence of genetic interactions (epistasis) on the genetic variance of quantitative traits is a major unresolved problem relevant to medical, agricultural, and evolutionary genetics. The additive genetic component is typically a high proportion of the total genetic variance in quantitative traits, despite that underlying genes must interact to determine phenotype. This study estimates direct and interaction effects for 11 pairs of Quantitative Trait Loci (QTLs) affecting floral traits within a single population of Mimulus guttatus. With estimates of all 9 genotypes for each QTL pair, we are able to map from QTL effects to variance components as a function of population allele frequencies, and thus predict changes in variance components as allele frequencies change. This mapping requires an analytical framework that properly accounts for bias introduced by estimation errors. We find that even with abundant interactions between QTLs, most of the genetic variance is likely to be additive. However, the strong dependency of allelic average effects on genetic background implies that epistasis is a major determinant of the additive genetic variance, and thus, the population’s ability to respond to selection.Copyright ©2015 Monnahan, Kelly. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are creditedhttp://creativecommons.org/licenses/by/4.0/EpistasisGenetic lociPopulation geneticsEvolutionary geneticsCorollaFlowersAllelesVariant genotypesArticle10.1371/journal.pgen.1005201openAccess