Trough =?

Context:

Geneticists have used this model to look for genetic segments surrounded by "troughs" of low variation, the theoretical footprint of a selective sweep. Applying the model has identified more than 2,000 genes -- roughly 10 percent of the human genome -- suggesting that selective sweeps were a frequent occurrence that drove the evolution of humans away from their primate ancestors.

The selective sweep model was introduced in 1974 and has pretty much been the central model ever since," Przeworski said. "It is fair to say that it is the model behind almost every scan for selection done to date, in humans or in other organisms."

However, areas of low diversity around gene segments might also be produced by other evolutionary mechanisms. To test whether selective sweeps were the predominant cause of these troughs, a group of scientists from the University of Chicago, the University of California at San Francisco, Hebrew University of Jerusalem, and the University of Oxford used data from179 subjects in the 1000 Genomes Project, an international effort to catalogue human variation.

More:
http://www.sciencedaily.com/releases/2011/02/110217141307.htm