Variation Catches a Ride

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Science  15 Oct 2010:
Vol. 330, Issue 6002, pp. 326-327
DOI: 10.1126/science.1197700

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Evolutionary change often involves what geneticists call quantitative traits—traits such as height, weight, or skin color that are determined by more than one gene and vary “continuously” or “semicontinuously” within a population (when graphed, the variation in the trait often resembles a bell-shaped curve). Quantitative traits are involved in many human diseases and in breeding economically important plants and animals; as a result, researchers are interested in understanding the underlying causes of their variation. Geneticists are getting ever closer to pinpointing the locations of the genetic variants that cause variability in quantitative traits, thanks to increasingly detailed studies of genomes that identify naturally occurring variants at individual chromosomal sites, especially differences at single-nucleotide sites in the DNA sequence (single-nucleotide polymorphisms, or SNPs) (1). There has been every reason to suppose that quantitative trait variation is subject to the same evolutionary forces that affect other types of DNA sequence variability, primarily by effects on the genes concerned through selection on a specific trait. On page 372 of this issue, Rockman et al. (2) test this idea and find that evolutionary mechanisms that target larger regions of the genome are more prominent than expected.