A method is provided for identifying one or more regions within a genome of an organism of interest that mediate the expression of one or more genes of interest. The method comprises identifying a first organism of interest exhibiting a measurable response to an environmental stimulus; identifying a second organism of interest that lacks or does not exhibit as strong a response to the stimulus as compared with the first organism of interest; crossing the first and second organisms of interest to produce a population of progeny; extracting RNA from each individual population of progeny; quantifying a level of gene expression for one or more genes of interest that are associated with the response to an environmental stimulus; identifying one or more Quantitative Trait Locus (QTL), wherein gene expression level is a quantitative trait, and using one or more markers comprising one or more regulatory sequences to mediate said expression of said one or more genes of interest induced by said environmental stimulus; and identifying the one or more regulatory sequences located at said one or more QTL.