NEW YORK (AP) — Researchers have cloned an adult mammal for the first time, an astonishing scientific landmark that raises the unsettling possibility of making copies of people.
Scientists slipped genes from a 6-year-old ewe into unfertilized eggs and used them to try to create pregnancies in other sheep. The result: A lamb named Dolly, born in July, that is a genetic copy of the ewe.
The feat opens the door to cloning prized farm animals such as cattle, and should make it much easier to add or modify genes in livestock, experts said.
It’s also scientifically stunning. Researchers used DNA from the ewe’s udder cells, proving that mature mammal cells specialized for something other than reproduction could regenerate an entire animal.
Experts said the same technique might make it possible to clone humans, but emphasized that it would be unethical to try.
“There is no clinical reason why you would do this. Why would you make another human being?” said Ian Wilmut, one of the scientists who cloned the sheep. “We think it would be ethically unacceptable and certainly would not want to be involved in that project.”
Carl Feldbaum, president of the Biotechnology Industry Organization, which represents about 700 companies and research centers in the United States and abroad, agreed.
“I can think of no ethical reason to apply this technique to human beings, if in fact it can be applied,” he said Sunday.
“The biotechnology industry exists to use genetic information to cure disease and improve agriculture. We opposed human cloning when it was a theory. Now that it may be possible, we urge that it be prohibited by law.”
A report of the sheep cloning will be published in Thursday’s issue of the journal Nature by Wilmut and colleagues at the Roslin Institute near Edinburgh, Scotland, and others.
Before the new work, scientists had been able to take tissue from adult frogs and create genetically identical tadpoles. But the tadpoles never developed fully into frogs.
To do the sheep cloning, scientists took cells from the ewe’s udder tissue and cultivated them in a lab, using a treatment that made the cells essentially dormant. They also took unfertilized sheep eggs and removed the nucleus, the cells’ central control room that contains the genes.
Then they put the udder cells together with the egg cells and used an electric current to make them fuse. The eggs, now equipped with a nucleus, grew into embryos as if they’d been fertilized. The embryos were put into ewes to develop.
The process was horrendously inefficient. Of 277 fused eggs, only one led to a lamb.
Wilmut said he expects the efficiency to improve. Someday a dairy farmer, for example, might make a few clones of cows that are especially good at producing milk, resisting disease and reproducing, he said.
A farmer wouldn’t want entire herds of identical animals, because populations need a diverse genetic makeup, he said. Without that diversity, a lethal disease that struck one cow might wipe out all the clones, too.
The advance will also provide a much more efficient way to insert genes into livestock, Wilmut and others said. Inserted genes can be used to make animals secrete valuable drugs in their milk, for example.
Scientists currently insert genes into fertilized eggs in a laboratory, which is a very inefficient way to produce animals that use the genes properly.
With the new technique, they start with a virtually unlimited supply of body cells from an adult animal, use a much more effective lab technique to insert genes, identify cells that use the genes as planned, and fuse them to eggs.