"It doesn't have to be, you know, embryo stem-cell research or fetal or cloning, " Lott said.
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' Another idea is to take a single cell from a developing embryo and then let that develop and see if those couldn't be used to derive stem cells.
Sir Ian and his team fused the genetic information from an adult sheep cell nucleus with an egg cell to form an embryo that developed into a genetically identical copy of the original adult.
In this new study, detailed this week in the journal Nature Methods, Hufnagel and colleagues recorded the movements of every cell nucleus in the embryo not only during the later developmental stages, but also throughout the first three hours of the embryo's life, when nuclei divide very rapidly.
In PGD, a cell is removed from the embryo for genetic testing to detect x or y chromosomes.
"A human embryo starts out as a single fertilised cell and rapidly divides into a widely complex series of cells that become a human being, " explained Dr McCallion.
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The success rate for creating an embryo by injecting DNA from a donor cell into an egg was 1 in 15, far more than researchers had previously thought possible.
Once you've got them, you don't need to destroy any more embryos, but each time you get a new one of these embryonic stem-cell lines, you need to destroy an embryo.
Reproductive cloning, which created Dolly the sheep in 1997, involves transferring the nucleus of an adult cell into an egg, giving the resulting embryo a full set of genes without the normal sperm-meets-egg fertilisation step.
They used stem cells from a human embryo, which are capable of becoming any other type of cell in the human body from nerve to skin, muscle to kidney.
Scientists using this method seek to persuade the cell to "forget" its current status and go back to the original stem cell state it was in during its time in the embryo.
"Nuclear transfer is really about the ability to take an adult cell and basically reprogram it so that you can grow an embryo from it, " Earp says.
On Thursday a team of researchers at Newcastle University in the UK, which hopes to join South Korea in the forefront of stem cell research, also said they had successfully cloned an human embryo.
They would also like to push other stem-cell types, such as those found in the intestine, to the limit in their embryo experiments.
Groups opposed to stem cell work on embryos say the use of embryos is immoral and unnecessary, because the procedure destroys the embryo and because an alternative is available.
But critics of human cloning and stem cell extraction methods essentially believe a human egg that begins to divide for any reason should be considered an embryo, and a potential person, that deserves protection under the law.
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