Clone Advance: Sheep by the Dozen

SCIENTISTS have found a way to make hundreds of genetically identical sheep from cells in a laboratory dish, a step that could greatly improve the ability to tinker with genes of farm animals.

For the first time in mammals, scientists took cells from an animal and produced thousands of copies, and then used the copies to successfully impregnate sheep.

If the technique can be perfected, experts say, it would be a major gain in the ability to make genetic changes in livestock for research and to quickly produce animals that give more or better milk or meat, and resist illness.

"It is a great achievement," commented Robert Foote, professor emeritus of animal physiology at Cornell University in Ithaca, N.Y. The work was reported this week in the journal Nature by Ian Wilmut, Keith Campbell and colleagues at Scotland's Roslin Institute near Edinburgh.

Currently, scientists can produce genetically identical farm animals by such techniques as breaking a single embryo into pieces and implanting each piece in a womb to form a new animal. But that approach yields fewer than 20 copies, rather than hundreds. The new technique can generate thousands of cells, giving scientists many more chances to achieve successful gene transfers.

Wilmut doesn't know if it would work in people, but he adds that many scientists would consider this application unethical.