Somatic cell nuclear transfer
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In genetics, somatic cell nuclear transfer (SCNT) is a technique for cloning.
The process
The nucleus of a cell contains DNA, which acts roughly as its blueprint (although unlike an actual blueprint, these instructions are greatly affected by environment as well as other factors not yet fully understood and can change over time). In somatic cell nuclear transfer the nucleus of an unfertilized egg is removed or destroyed. The nucleus of a somatic cell (a cell other than a sperm or egg cell) is then removed and put in the emptied egg.
This technique is currently the basis for cloning animals, such as the famous Dolly the sheep, and could theoretically be used to clone humans. It is commonly used to produce embryonic stem cells. In order to do this, the egg, now containing the nucleus of a somatic cell, is stimulated in such a way that it begins to divide. The resulting cells are, ideally, genetically identical to the original; embryonic stem cells are harvested when dividing cells have formed a blastocyst.
Limitations
The stress placed on both the egg cell and the introduced nucleus are enormous, leading to a high mortality rate in resulting cells. As the procedure currently cannot be automated, but has to be performed manually under a microscope, SCNT is very resource intensive.
The biochemistry involved in "activating" the recipient egg is far from understood.
Not all of the donor cell's genetic information is transferred. DNA of organelles (mostly mitochondria) is left behind, with the resulting cells retaining those structures which originally belonged to the egg.de:Zellkerntransfer