Comparing Chimp and Human DNA

In a new study, published online in the open-access journal PLoS Genetics, Katherine Pollard, at the UC Davis Genome Center, and colleagues at UC Santa Cruz led by David Haussler used comparative genomics to investigate the properties of a set of 202 carefully screened “highly accelerated regions” (HARs).

The authors searched for stretches of DNA that were highly conserved between chimpanzees, mice, and rats, comparing those sequences to the human genome sequence in order to unravel the evolutionary forces at work behind the human genome’s fastest evolving regions.

Pollard explains that “most of the differences between chimps and humans are not in our proteins, but in how we use them.” Only three HARs lie in genes that are likely to encode proteins. The rest do not appear to code for genes at all; instead, many HARs are located close to genes involved in growth and development. The most dramatically accelerated region, HAR1, appears to make a piece of RNA that may have a function in brain development.

“They’re not in genes, but they’re near genes that do some very important stuff,” Pollard said. Typically, non-coding regions of DNA evolve more rapidly than regions carrying genes because there is no selective pressure to stop mutations from accumulating. However, the human-accelerated regions are highly conserved across the other groups of animals that the researchers examined, suggesting that they have important functions that stop them from varying too much.

This study was funded by the National Institutes of Health and the Howard Hughes Medical Institute.