Cloning

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Starting

For the first time, scientists have created human embryonic stem cells by transferring the nucleus of a mature cell into an egg. The cloningtechnique could nudge the dream of personalized medicine closer to reality.

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Danger

"The animals produced by cloning are abnormal," he says. "Most scientists who practice nuclear transfer think it's unethical and unsafe to try human reproductive cloning."

-Meghan Rosen