Epistasis plays a dominant role in the genetic architecture of Drosophila quantitative traits. Wen Huang¹, Robert Anholt², Trudy Mackay¹. 1) Department of Genetics, North Carolina State University, Raleigh, NC; 2) Department of Biology, North Carolina State University, Raleigh, NC.

   Genetic interaction or epistasis is important for canalization and speciation. However, the role of epistasis in controlling quantitative trait variation remains controversial. We performed genome-wide screens for single nucleotide polymorphisms (SNPs) associated with three life history traits (starvation resistance, startle response, and chill coma recovery time) in the recently developed Drosophila melanogaster Genetic Reference Panel (DGRP) and in a synthetic outbred population, derived from this panel through advanced intercrossing (Flyland). The genetic architecture for all three traits was highly polygenic in both the DGRP and the Flyland populations. Although there was no overlap between SNP associations in the two populations, genes associated with the quantitative traits in either population were highly connected in common epistatic networks. Furthermore, population/background specific associations could be explained by changes in allele frequencies of many SNPs that constituted the genetic contexts through epistasis in the two populations. We extended the analysis to all pair-wise interactions between SNPs in the genome and found extensive epistasis. Particularly for chill coma recovery, there was a marked enrichment of significant single SNP associations among SNPs participating in pair-wise interactions. In addition, we also showed by simulation that epistasis could induce substantial additive variance. Taken together, these results suggest a dominant role of epistasis in the genetic architecture of Drosophila quantitative traits, with additivity an emergent property from underlying epistatic genetic architecture.