French scientists have sidestepped a physiological quirk and successfully cloned the rat, an animal commonly used as a model in laboratory research.

The list of animals producing live-born clones has grown to include:

• sheep
• cow
• mule
• pig
• goat
• rabbit
• cat
• mouse

Until now, the rat had been difficult to clone because rat eggs start dividing almost as soon as they are removed from a female's body.

Albino lab ratCourtesy: Eric Murphy, Washington State University

The early division prevents scientists from inserting the necessary donor DNA from an adult cell.

Developmental biologist Jean-Paul Renard of the national institute for agronomic research near Paris was able to accomplish the feat.

His team used a drug to inhibit cell division, which gave them time to manipulate the cells. Their study appears in Friday's online issue of the journal Science.

"The first born was called Ralph," said Renard. He said the other clones have no names.

"It's now the policy of my lab not to give names to clones because they are experimental animals."

The researchers reported 129 cloned embryos were implanted in female rats and three male pups were born. One pup later died.

Since Ralph and his copy were born last November, they've produced apparently healthy pups.

The cloning is big news for physiology research because albino rats are widely used as laboratory models for human disease.

The researchers see the cloned rats as the first step towards genetic modification of the animals.

Combined with the nearly complete rat genome, Renard says the clones may allow researchers to further their studies on heart disease and Alzheimer's disease.