In therapeutic cloning, the host egg is first isolated in a petri dish. The outer cell wall is then penetrated without destroying the egg, and a tiny pipette is used to gently suck the nucleus, with the host’s DNA, out of the cell in the same way one might pit an extremely tiny olive. The result is a hollow structure called an enucleated cell. The empty space within the host cell is quickly injected with a nucleus from the cell of the donor. (Alternatively, the donor cell can be placed in extremely close proximity and fused with the host cell by means of an electrical pulse.) Now the host cell’s mechanisms have essentially been "reprogrammed" to make copies based on the new nucleus’ genetic codes. (Holland et al 2006)
If ibis procedure were to be used for reproductive cloning, the egg would be stimulated to begin dividing and developing. The newly created embryo would be genetically identical to the donor source of DNA. The resulting offspring would have only one genetic parent with whom it shares all its genes. Once reaching the blastocyst phase, the embryo can be implanted in a womb to develop naturally. In therapeutic cloning, the embryo is also stimulated to begin dividing. Hut the cells will never be implanted in a womb. Instead, the embryonic stem cells are taken from the inner cell mass of the embryo, when it has formed info the ball-shaped blastocyst stage of just a couple of hundred cells.
The technology does not exist for doing this without tearing apart the delicate blastocyst. (Holland et al 2006) The procedure, which is not too unlike shelling extremely delicate peas from a microscopic pod, must necessarily puncture and destroy the embryo. This allows the precious cargo of stem cells to spill out for collection into the petri dish medium like a handful of jewels strewn on a blood-red carpet. One of the major biological concepts overturned by the therapeutic cloning process is that once cells have differentiated, they cannot be induced to revert. Yet in this one circumstance, the rules have been broken. The isolated nuclei of an adult donor cell can revert back to pluripotency by being exposed to the inside of an egg. (Holland et al 2006) In effect, this creates a fertilized egg with the donor’s genetic complement without going through the process of fertilization.
