1. A method for identifying a quantitative trait locus for a complex trait that is exhibited by a plurality of organisms in a population, comprising: (a) dividing said population into a plurality of sub-populations using a classification scheme that classifies each organism in said population into at least one of said sub-populations, wherein said classification scheme is derived from a plurality of cellular constituent measurements for each of a plurality of respective cellular constituents that are measured from each said organism; and (b) performing, for at least one sub-population in said plurality of sub-populations, quantitative genetic analysis on said sub-population in order to identify said quantitative trait locus for said complex trait; wherein said dividing step (a) and performing step (b) are executed using a suitably programmed computer.