Saturday, March 1, 1997

Clones, like twins, would not be an exact match

By FAYE FLAM

Knight-Ridder Newspapers

The recent cloning of a Scottish sheep raised one big question in the public consciousness: What would happen if someone tried cloning a human being - growing a human baby from a cell taken from an adult man or woman?

Ethicists are appalled by the idea, and scientists are not yet sure it's even possible. But, were it to be done, such an experiment would produce something we've all seen before, an identical twin. Cloning is simply a way of artificially inducing the birth of identical twins.

The only difference is that if scientists could do in humans what they did in cloning sheep, the new twin could be much younger than the original one.

A person could parent an identical twin of himself or herself.

But a clone would not be a copy of its parent/donor, any more than pairs of twins are double versions of the same persons.

"I talk to pairs of twins all the time, and they are different people," says psychologist Margaret Keyes, who studies identical twins at the University of Minnesota. The work she and her colleagues have done shows twins share about 50 percent of measurable personality traits.

That means a clone might be more outgoing, or more determined or lazier than its parent.

A clone of Elvis Presley or Pablo Picasso or Ernest Hemingway might not achieve the same fame. The clones would grow up in different environments, read different books, meet different mentors. They would think different thoughts.

And so, the cloned sheep, named Dolly, is still a unique sheep.

Thomas Bouchard, who also studies twins at the University of Minnesota, says he has witnessed dozens of first meetings of twins reared apart. At first, he says, the meetings "take their breath away," but within a few minutes, he says, they realize they are separate people.

"It is no threat to their sense of self."

There are only a few reasons anyone would ever try such an experiment, says medical ethicist Arthur Caplan of the University of Pennsylvania. Perhaps someone would want to replace a dying child, he says. Or someone might try to reproduce the talents and abilities of a concert pianist or a brilliant scientist.

Some might want to do it out of vanity.

Ethicists have already been thinking about the rules and laws we should impose on cloning, Caplan says, because scientists long suspected it was possible.

After all, every cell in the sheep body holds within it the same complete genetic blueprint for making it. But a variety of factors keeps all ordinary cells other than fertilized eggs from beginning to sprout into new sheep. (The same is true of humans.)

For the last few years scientists have been able to clone mice, sheep and cattle by taking a cell from a tiny embryo - in essence artificially inducing the same sort of divisions that produce natural twins. But no one had come close to cloning from the cell of an adult animal.

Scientists still don't fully understand how the fertilized egg "knows" how to divide into a complex creature, giving rise to some cells that seem to know to become bone, others muscle and skin, all laid in just the right places.

There's something in the chemistry of the cell that tells the DNA what to do, says Ralph Brinster of the University of Pennsylvania's Veterinary School. "But nobody knows exactly what happens."

The Scottish researchers used a cell from the sheep's mammary gland to grow Dolly. They took out the nucleus of the cell, which holds its DNA, and put it into what was an unfertilized egg cell but with its own DNA removed.

They adjusted the chemistry of the cell and adjusted the timing of the cell cycle, and managed to trick the DNA into starting up a new sheep.

Biologist Karl Evert from Tufts University foresees benefits in medical research. With cloned lab animals, scientists could more precisely test new drugs. They could, for example, give a new drug to some members of a cloned family and compare the effects with identical animals not given the drug.

Penn's Brinster, who is noted for creating genetically engineered mice, agrees that the new finding may reveal the mysterious way that complex creatures emerge from single cells. But for all the fuss about the ethics of cloning humans, he says the possibility that anyone would go through with this is "highly unlikely."