A method for associating a gene with a trait exhibited by one or more organisms in a plurality of organisms from a species. A genetic marker map is constructed from a set of genetic markers associated with the plurality of organisms. For each gene in a plurality of genes, a quantitative trait locus analysis is performed using the genetic marker map and a quantitative trait. The quantitative trait locus analysis produces quantitative trait locus data. A quantitative trait comprises an expression statistic for a gene. The expression statistic for a gene is derived from a cellular constituent level that corresponds to the gene in each organism in the plurality of organisms. The quantitative trait locus data are clustered from each quantitative trait locus analysis to form a quantitative trait locus interaction map. Clusters of genes in the map are identified as a candidate pathway group. An expression cluster map is used to refine the candidate pathway group. Multivariate analysis is used to validate the candidate pathway group as a set of genes that are genetically interacting.