Nuclear transfer method: Nuclear transfer will extend the range of species in which gene targeting will be possible and thereby provide better models to test treatments for human diseases. The production of Dolly followed by subsequent confirmation in cow and mice successfully established a cloning technology, which have opened the new horizons of application of nuclear transfer technique in production of transgenic animals. Current available technique of pronuclear microinjection of a DNA expression cassette is inefficient and expression levels are unpredictable. Nuclear transfer (cloning) offers an appealing alternative. Hence, one could perform gene targeting in cell lines that is able to donate its nuclei to recipient oocytes. This would allow selection of the most productive cell line showing high expression for conversion into highly productive animals, and all animals will be transgenic. For example, the time from microinjection to a milk producing flock is 3.5 years, if the founder is female, and 2.5 years, if it is male. With somatic cloning this time can be reduced to 1.5 years. This saving of time will be greater with cow. Production of transgenic founder animals by nuclear transfer also uses less than half the number of experimental animals than a pronuclear injection.