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Cloning Human Embryos
Human cloning is an extraordinarily contentious issue. Cloning a human embryo involves taking a cell (or cells) from a pre-existing embryo and growing it into its own, separate embryo with identical DNA. The new embryo can develop either in vivo -- through implantation into a woman's uterus -- though there are laws against this in most countries, or in vitro (in, for example, a Petri dish). Cloning an embryo is like creating a twin, but through inducement, rather than a spontaneous, natural process.
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Possibilities of Embryonic Cloning
Human embryonic cloning could take two major directions. The first involves reproduction; the second involves harvesting stem cells to be transformed into specific cell types and this is known as therapeutic cloning.
Using cloning capabilities for reproduction would involve creating an embryo to be developed in vivo and born as a human. This is a potential solution for people who have no partner, who could theoretically birth and raise their own identical twins, and for couples who have fertility problems. It is doubtful whether societies would allow this and scientists engaged in therapeutic cloning find the idea as abhorrent as most people.
Stem Cell Research
The more well-known possibility that arises from embryonic cloning involves transforming the stem cells of a clone into specific cell types. An embryo's cells are "blank" stem cells, meaning that they can be altered to grow into any number of other cells. For example, treatment for a burn victim who needs a skin transplant could involve creating an embryo clone from one the victim's cells and then taking stem cells from this clone, bathing them in chemicals to produce new skin cells which are replicated until there are enough to complete a skin graft. As the cells are created with the patient's own DNA, there would be no immune reaction.
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Controversies of Embryonic Cloning
The possibilities of cloning embryos raise a number of ethical questions. Using embryonic cloning for reproductive purposes is questionable because the clone will be an identical replica of an existing person. This could be psychologically damaging for the clone -- especially if she is a clone of her mother! Further, creating a human from the genetic material of just one parent (rather than the combined genetic material of two parents) goes against the fundamental idea of conception as the joining of two individuals.
Cloning an embryo for the purposes of harvesting its cells is particularly controversial. The procedure involves creating an embryo, then using its cells to save a living human -- a process that necessarily destroys the embryo. The essential question is whether an embryo is considered "alive." If an embryo is categorized as a living human, killing it to harvest its stem cells for other purposes could be considered in some quarters as murder.
The word 'embryo' is also emotive as scientists are not using anything recognisable as human, but a collection of cells, no bigger than a punctuation mark, that are destroyed, usually after 6 days when it is at the blastocyst stage. Of course opponents argue that even this is wrong because a life has been started.