Research updates 65-year-old genetic discovery

Chimpanzees and humans have gene variant, for different reasons

TEMPE, Ariz. -- Gene variants determine which humans and which chimpanzees can taste bitter substances. For humans, this taste sensitivity may influence nutritional choices and ultimately their health, as well as behaviors, such as smoking. For chimpanzees, it provides a way to live safely in their environments by avoiding toxic plants and other harmful compounds.

Research conducted more 65 years ago by a team of scientists led by Sir Ronald Aylmer Fisher, the eminent British statistician and geneticist, concluded that this gene variant was the same in humans and chimpanzees and existed throughout time--an example of balancing selection. Their findings were published in 1939 in "Nature," one of the world's leading science journals.

A new team of researchers, including Anne Stone, an anthropological geneticist at Arizona State University, writes in the cover story of this week's "Nature" (April 13, 2006), that while the observations made by Fisher and his team were accurate, "their explanation was wrong." Instead of being an example of balancing selection, the researchers conclude that both humans and chimpanzees have gene variants but for different reasons--and is an example of convergent evolution.

It was only a few years ago, in 2003, that sensitivity to a bitter compound known as phenylthiocarbamide (PTC) was mapped in human genes.

"That gene was found to be controlling whether you can taste PTC or not," says Stone, an associate professor in ASU's School of Human Evolution and Social Change in the College of Liberal Arts and Sciences.

"We decided to look at this in chimpanzees and see if Fisher was right," she says. The "we" includes authors of the report Stephen Wooding, Michael T. Howard, Diane M. Dunn, Robert B. Weiss and Michael J. Bamshad in the Department of Human Genetics at the University of Utah; Bernd Bufe and Wolfgang Meyerhof of the German Institute of Human Nutrition Postdam-Rehbruecke; and Christina Grassi and Maribel Vazquez in the Department of Comparative Medicine at the Southwest Foundation for Biomedical Research.

Stone, who works on applications of population genetics to questions concerning the origins, population history and evolution of humans and the great apes, sent DNA samples of each of three subspecies of chimpanzees to the University of Utah.

"No chimpanzees were harmed to obtain the samples," Stone notes. The DNA is provided by veterinarians and comes from either blood samples or cheek swabs. She uses these samples to help zoos, sanctuaries and primate centers identify subspecies of chimpanzees.

"My goal is to better understand chimpanzees in their own right and to ultimately help with their preservation," she says.

Her samples contributed to this latest research, which found that when compared to human non-taster gene variants, "chimps don't have the same change in the middle of the gene variant as humans, but rather have a change at the start." Both changes in the sequences cause this bitter taste receptor not to work. These are the findings that demonstrate that while some humans and some chimpanzees can not taste this bitter substance, the reasons why are different.

Going forward, this new information can be used by researchers to understand bitter-taste receptors and how having particular bitter-taste receptors affect nutrition and health, Stone explains.

With this week's "Nature" cover story, Stone joins a growing list of researchers from ASU's College of Liberal Arts and Sciences whose research has made the cover of either "Nature" or "Science" this academic year.

While that's an exceptional achievement in itself, what's noteworthy is that three of the researchers are junior faculty--assistant or associate professors. Stone, an associate professor, joins Gro Amdam, an assistant professor, and Kevin McGraw, an assistant professor, on the list. Both Amdam and McGraw are in the college's School of Life Sciences.

Amdam's research found a link between social behavior and maternal traits in bees. A paper describing her experiments was the cover story of the Jan. 5 issue of "Nature," which she wrote with M. Kim Fondrk and Robert Page from ASU, and Angela Csondes from the University of California, Davis. Fondrk is a program manager and Page is a professor and director in the School of Life Sciences.

McGraw's research showed that the female North American barn swallow, even after pairing with a male, still comparison shops for sexual partners. His study was featured on the Sept. 30, 2005, cover of the journal "Science."

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SOURCE:
Anne Stone, acstone@asu.edu (480) 727-6310


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