Scientists outline genome of the rat

ASSOCIATED PRESS

Scientists have published nearly the entire genome of the common rat, making it possible to compare it with the genetic maps of people and mice. That ability is expected to yield clues about evolution and the biology of disease.

The genome of the brown Norway rat, which thrives everywhere from subways to cornfields, is 5 percent smaller in volume than its human equivalent and slightly larger than the mouse.

About 90 percent of its estimated 25,000 to 30,000 genes have counterparts in humans and mice.

Gary Churchill, a senior scientist at the Jackson Laboratory in Bar Harbor, Maine, said having the genetic sequences of two closely related mammals such as mice and rats would arm scientists with more genetic information than either would alone, when comparing with humans.

“If you can look at mouse and rat and see that they’re the same, you have a much greater likelihood that it’s going to be relevant across species,” said Mr. Churchill, who was not part of the study. “The leap isn’t so far.”

Other scientists said that, genetically speaking, rats are not simply bigger mice. They predicted the differences between the rodent species would be valuable, too.

“They are much further apart in evolution than we are from some monkeys,” said Ian Jackson of the MRC Human Genetics Unit in Edinburgh, Scotland. “In some respects, they are better than mice in behavioral tests. They seem to be smarter. The rat genome should be a great help in tracking down genes that affect behavior.”

The research was performed by the Rat Genome Sequencing Project Consortium and funded by the National Human Genome Research Institute and the National Heart, Lung and Blood Institute. The results are in today’s issue of the journal Nature.

Scientists said all three species probably inherited genes from a common mammalian ancestor about 75 million years ago, not long before dinosaurs went extinct and surviving mammals quickly took their places.

But there are some key differences. For example, the rat relies more heavily on its sense of smell than humans, and it has more genes devoted to scent detection.