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02/22/2006 Finding answers to ancient genetic questions

By Stephanie Schupska
University of Georgia

Millions of years. That's the time period Andrew Paterson works with in his research. He’s searching for clues as to why a certain plant turned out the way it did, why a certain gene was preserved and another discarded.

His current research at the University of Georgia centers on polyploids, organisms that have twice the normal number of chromosomes. His findings were published online Feb. 8 in the “Proceedings of the National Academy of Sciences of the United States of America” (PNAS).

“We each have one chromosome from mom and one from dad,” said Paterson, director of UGA's Plant Genome Mapping Laboratory. “Once in a long while, the reproductive process makes an error. It makes four, two from each parent. Only a fraction of these organisms survive.”

Plants are much more tolerant of such errors than animals. By studying those plants that have survived, Paterson hopes to find answers to which extra genes a plant keeps and which it discards, a choice that continues to shape the world.

“I think there will be quite a lot of interest in this research,” Paterson said of the study of polyploids. “People are realizing that polyploids are more common than they thought. It was surprising that rice was an ancient polyploid. I think that the role of genetic duplication and polyploidy in evolution has generally been underestimated.”

Paterson's PGML colleague, John Bowers, built the groundwork; and former UGA graduate student Brad Chapman started the present experiment in 2003 as part of his dissertation. Paterson’s lab is doing a follow-up study to “ask what happens to genes after they're duplicated,” he said. “Dr. Bowers’ research set the structure for asking questions.”

Before Paterson published his study, scientists believed that polyploid genes would change quickly. “We found the opposite, that duplicated genes change slowly,” he said.

In his article, Paterson says that “genome duplication, a punctuational event in the evolution of a lineage, is more common than previously suspected.” At the same time, he says, there is actually less species-wide polymorphism than scientists had thought.

This particular study centers on rice and Arabidopsis, a small flowering plant commonly called thale cress or mouse-ear cress. It’s related to cabbage and mustard. These plants were traditionally thought to be diploids. But Bowers, Paterson and Chapman showed them to be ancient polyploids.

Paterson said major crops such as cotton, wheat, soybeans, maize (corn), sugar cane, alfalfa, potatoes, tobacco and some grasses are recent polyploids. They genetically mutated from 10,000 to a few million years ago.

Research suggests that all plants, and even mammals, may be ancient polyploids, he said. In recent years, scientists have successfully made artificial polyploids. This work could lead to their more effective use to improve crops.

(Stephanie Schupska is a news editor with the University of Georgia College of Agricultural and Environmental Sciences.)

(Stephanie Schupska is a news editor with the University of Georgia Public Affairs Office.)

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