Since Scottish researchers created Dolly in 1997 by placing an adult ewe's genes in an empty egg and triggering it to develop into an embryo, other scientists have managed to clone worms, mice and cattle using the same methods. But the failure rate has been alarmingly high at 98 percent.
　　Often the attempts have resulted in failed births or clones with genetic defects such as extra large organs or weak hearts or immune systems.

"Cloning is a hit-or-miss affair right now," says Ron Green, an ethicist and religion professor at Dartmouth College.

There are also complications that arise when dealing with people rather than animals, including how to prevent the birth of a badly deformed baby.

Catching Problems in Time

Panayiotis Zavos of the University of Kentucky, the scientist who announced his intention to clone, has said he and his colleagues stop any pregnancy that appears to be going wrong by abortion.

But, Green argues, flaws may not always be apparent.

"Many of the problems that have arisen in animal tests have been mostly unobservable at [the fetus] level," he says. "Then you'll have a sick child you can't simply dispose of."

Zavos counters there is a real need for human cloning technology, particularly among parents who are unable to conceive by any other means. And, he claims, there is a responsible way to do it.

"We just have to approach this project with a lot of T.L.C.," he told ABCNEWS. "And we know exactly how heavy this undertaking is."

(From abcNews.com)