Animal Cloning:
When entire animals are obtained from somatic cells of an animal, it is known as animal cloning. Cloning is usual in plants but in case of animals only some degree of success had been achieved so far. In previous, nuclei from a tadpole were transplanted into the cytoplasm of an enucleated fertilized frog egg, and normal frogs were obtained. But in 1997 British scientists got success in cloning of sheep by transferring the nucleus from an udder cell of an adult sheep into the cytoplasm of a enucleated fertilized egg. Then the egg was transplanted into the uterus of a surrogate mother where it developed like a normal zygote into a normal lamb which has grown now into a normal adult sheep.
Udder cells from an adult sheep were primary cultured in vitro. The cultured cells were caught in the Go phase (quiescent stage) and then fused in vitro with enucleated ova of right stage. The fusion products were cultured in vitro before it transfers into the uteri of surrogate mothers. The chance of success in obtaining normal embryo developed is rather low.
In many situations, cloning is highly desirable since allows indefinite multiplication of an elite desirable without the risk of segregation and recombination during in meiosis, that must precede sexual reproduction. Clearly, the technique holds great promise in genetic research, mainly in understanding aging and curing genetic diseases. The technique need to be refined and expanded to other animals. However, in most of the countries, mainly in all developed countries, human cloning is prohibited.
Following the above report American scientist announced successful cloning of rhesus monkey using splitting technique; this is the closest species to humans where embryo splitting has been successful.