A very nice paper by Carlborg et al. in Nature Genetics demonstrates that the genetic architecture of a major locus for growth in chicken can be attributed to a genetic network of four interacting loci. My prediction is that we will see more examples of this in model systems, agricultural species, and in humans over the next few years. Studies like this support Alan Templeton's statement that epistasis will be uncovered when properly investigated (see his chapter in Epistasis and the Evolutionary Process).
Carlborg O, Jacobsson L, Ahgren P, Siegel P, Andersson L. Epistasis and the release of genetic variation during long-term selection. Nature Genetics, March 12 (2006) [PubMed]
It is an enigma how long-term selection in model organisms and agricultural species can lead to marked phenotypic changes without exhausting genetic variation for the selected trait. Here, we show that the genetic architecture of an apparently major locus for growth in chicken dissects into a genetic network of four interacting loci. The interactions in this radial network mediate a considerably larger selection response than predicted by a single-locus model.