Scientists and corporations have been cloning mammals for about 10 years . Up until recently, scientists have only been able to use DNA taken from embryo cells in order to clone animals. However, with recent advances, scientists no longer have to limit themselves to embryo cells for cloning. For instance, Dolly was cloned from DNA taken from udder cells, rather than embryonic cells. The DNA, once removed, is inserted into the nucleus of an egg cell, which is then put into a surrogate mother .
Cloning is important for biotech companies.
For example, these companies are trying to make genetically engineered sheep that produce valuable blood clotting elements and other pharmaceuticals in their breast milk. These sheep become essentially bio-reactors , producing valuable pharmaceuticals. Once the researchers go all the trouble to create such sheep, they can't allow the sheep to reproduce naturally, because normal reproduction would bring in random gene selection. Consequently not all the offspring would be able to produce the pharmaceuticals. The sheep are therefore cloned.