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    The Facts and Fiction of Cloning

    Understanding the real science behind the headlines and the hubbub.

    What Is Cloning? continued...

    Understanding Cloning

    In nuclear transfer, DNA from an unfertilized egg is removed and replaced with DNA from an adult body cell -- a skin cell, for example. When the process works, the manipulated cell -- coaxed by the newly-implanted genetic material -- begins to divide and eventually becomes a genetic replica of the adult-cell donor. The process produces a new individual whose identical twin is not a minute or two older, but already grown up.

    Now, researchers in South Korea and the University of Michigan have cloned a human embryo. This is not cloning to make a genetically matched baby, but cloning for research purposes -- also called therapeutic cloning or research cloning.

    This new development means that therapeutic cloning -- the ability to create human clones for research purposes -- is no longer a theory, but a reality. And it's sure to reignite the controversy of whether to ban all cloning or to allow some cloning for therapeutic purposes.

    Therapeutic cloning is not new. Scientists have used the technology to cure a variety of diseases in mice. Scientists have also studied the potential uses of human stem cells culled from embryos leftover in fertility clinics.

    Embryo Successfully Cloned

    Previous attempts to clone human embryos to obtain stem cells genetically identical to the patient are believed to have failed despite reports to the contrary -- until now.

    In this new study, researchers collected 242 eggs donated by 16 South Korean volunteers. Each woman also donated some cells from her ovary.

    The scientists then used a technique called somatic nuclear transfer to remove the genetic material -- which contains the nucleus of each egg -- and replace it with the nucleus from the donor's ovarian cell.

    Then, using chemicals to trigger cell division, the researchers were able to create 30 blastocysts -- early-stage embryos that contain about 100 cells -- that were a genetic copy of the donor cells.

    Next, the researchers harvested a single colony of stem cells that have the potential to grow into any tissue in the body. Because they are the genetic match to the donor, they aren't likely to be rejected by the patient's immune system.

    "Our approach opens the door for the use of these specially developed cells in transplantation medicine," says Woo Suk Hwang, a scientist who led the research in South Korea.

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