Scientists Decode Chimp DNA

An international team of scientists led by researchers from the Broad Institute of MIT and Harvard as well as Washington University in St. Louis recently completed a genetic map of the chimpanzee and discovered that chimp DNA is 96 percent identical to that of humans.

Scientists said that the findings, which were published on Sept. 1 in the journal Nature, could help them understand why diseases such as Alzheimer’s, AIDS, malaria, and certain cancers are more prevalent and severe in humans than in chimpanzees and other great apes.

“Because the chimp is so close, its physiology is remarkably similar, so that provides us with a way of looking at ourselves in a different context,” said Robert H. Waterston, chair of the Department of Genome Sciences at the University of Washington, who worked on the project. “And more importantly, in places where the chimp differs from humans in physiology and response to disease, we can use genetic differences to figure out what is going on.”

For example, chimpanzees contract HIV, but unlike humans, they do not develop full-blown AIDS, Waterston said. Further studies of the genome could explain why they do not experience the same symptoms.

The project, titled The Chimpanzee Sequencing and Analysis Consortium, involved 67 scientists from five countries. It found 40 million DNA base pair differences in the two genetic codes that resulted from either random mutations or complete insertions and deletions of DNA. However, researchers said many of these differences may have no function.

“It is likely that the vast majority of these genetic differences do not influence human biology, and we expect that in the next few years we will be able to find perhaps a few hundred thousand potentially interesting changes,” the study’s lead author, Tarjei S. Mikkelsen of the Broad Institute, wrote in an e-mail.

This relatively low number of significant variations, which have occurred since chimps and humans evolved from a common ancestor six million years ago, leaves almost 99 percent of human DNA identical to the chimp genome.

“It didn’t take many more genetic changes to evolve modern humans than it did to evolve modern chimpanzees,” Mikkelsen wrote.

That one percent, though, is responsible for important differences in the anatomy, behavior, and cognitive skills of the two species, Mikkelsen added.

“For example, all humans are capable of learning to speak a complex language, whereas chimpanzees appear to be fundamentally unable to do so,” he wrote.

While the sequencing of chimpanzee DNA is an important first step, researchers must sift through more data in order to pinpoint which genetic differences explain the particular biological functions unique to chimps and humans.

These investigations “are likely to keep scientists busy for decades to come,” Mikkelsen wrote.

—Staff writer David Zhou can be reached at dzhou@fas.harvard.edu