Cloning to reproduce desired genotypes

Cloned sheep, cattle, goats, pigs and mice have now been produced using som atic cells for nuclear transplantation. Animal cloning is still very ineffi cient with on average less than 10% of the cloned embryos transferred resul ting in a live offspring. However successful cloning of a variety of differ ent species and by a number of different laboratory groups has generated tr emendous interest in reproducing desired genotypes. Some of these specific genotypes represent animal cell lines that have been genetically modified. In other cases there is a significant demand for cloning animals characteri zed by their inherent genetic value, for example prize livestock, household pets and rare or endangered species. A number of different variables may i nfluence the ability to reproduce a specific genotype by cloning. These inc lude species, source of recipient ova, cell type of nuclei donor, treatment of donor cells prior to nuclear transfer, and the techniques employed for nuclear transfer. At present, there is no solid evidence that suggests clon ing will be limited to only a few specific animals, and in fact, most data collected to date suggests cloning will be applicable to a wide variety of different animals. The ability to reproduce any desired genotype by cloning will ultimately depend on the amount of time and resources invested in res earch. (C) 2000 by Elsevier Science inc.