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Producing identical pigs for research.

Cloning is the process of producing genetically identical plants or animals. For many plant species, this is a simple procedure just take a cutting and allow it to root in damp sand. In others, single cells can be grown in culture and entire new plants produced by manipulation with hormones.

Cloning is more difficult in animals. Almost every animal cell contains a nucleus, each of which has identical genetic information. Therefore, in theory, each cell could be cultured to produce an entirely new individual that would be genetically identical to the donor animal. The problem is that animal genes controlling the development of new individuals appear to "switch off" after a certain stage and, at present, can not be "switched on" again.

Researchers at the University of Missouri-Columbia have overcome this by taking genetic material from cattle and pig embryos at the eight cell-blastocyst stage. They suck the nucleus out of a blastocyst cell with a micro-pipette while holding it by suction under a microscope, then use this nucleus to replace that of an unfertilized ovum.

The new composite cell next is treated to fuse the protoplasm and seal the cell membrane, then cultured in vitro. In theory, eight identical animals can be produced from each blastocyst. If the process is repeated when the new cells reach the eight-cell stage, 64 identical cells can be created. After a third cycle, there could be 256.

When enough genetically identical blastocysts have been cultured, they are implanted inside a surrogate uterus and allowed to grow to term. Since the technology still is being perfected, many manipulated embryos fail to develop properly. So far, the technique has yielded hundreds of is to produce identical pigs for research purposes, but there are practical applications. Clones of superior animals could help to improve the rate of genetic gain in cattle and swine.
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Publication:USA Today (Magazine)
Date:Jun 1, 1993
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