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...