Selective Sweep - Involvement in Agriculture and Domestication

Involvement in Agriculture and Domestication

Rarely are genetic variability and its opposing forces, including adaptation, more relevant than in the generation of domestic and agricultural species. Cultivated crops, for example, have been essentially genetic engineered for more than ten thousand years, subjected to artificial selective pressures, and forced to adapt rapidly to new environs. Selective sweeps, provide a baseline from which different varietals could have emerged.

For example, recent study of the corn (Zea mays), genotype, uncovered dozens of ancient selective sweeps uniting modern cultivars on the basis of shared genetic data possibly dating back as far as domestic corn’s wild counterpart, teosinte. In other words, though artificial selection has shaped the genome of corn into a number of distinctly adapted cultivars, selective sweeps acting early in its development provide a unifying homoplasy of genetic sequence. In a sense, the long-buried sweeps may give evidence of corn’s, and teosinte’s, ancestral state by elucidating a common genetic background between the two.

Another example of the role of selective sweeps in domestication comes from the chicken. A Swedish research group recently used parallel sequencing techniques to examine eight cultivated varieties of chicken and their closest wild ancestor with the goal of uncovering genetic similarities resultant from selective sweeps. They managed to uncover evidence of several selective sweeps, most notably in the gene responsible for thyroid-stimulating hormone receptor (TSHR), which regulates the metabolic and photoperiod-related elements of reproduction. What this suggests is that, at some point in the domestication of the chicken, a selective sweep, probably driven by human intervention, subtly changed the reproductive machinery of the bird, presumably to the advantage of its human manipulators.