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Animal Cloning
When complete animals are obtained from somatic cells of an animal, it is called animal cloning, Earlier, nuclei from a tadpole were transplanted into the cytoplasm of an enucleated fertilized frog egg, and normal frogs were obtained. But early in 1997, British scientists announced successful cloning of sheep by fusing an udder cell of an adult sheep with an eunucleated fertilized egg.

The egg was then transplanted into the uterus of a surrogate mother where it developed into a normal lamb, which grew into a normal adult sheep, called 'Dolly'.

Cells from mammary gland of an adult sheep (6 yr-old ewe) were first cultured in vitro. The cultured cells were induced to enter Go phase (quiescent stage) by reducing the concentration of serum in the medium from 10% to 0.5% for 5 days. The Go cells were then fused in vitro with ennucleated ova of appropriate stage.
Cell fusion was induced by electrical pulse, which also activated the oocyctes. The fusion products were cultured in vitro in ligated oviducts of sheep up to morula or blastula stage, before their transfer into the uteri of surrogate mothers.

The rate of success in obtaining normal embryo development was rather low: a total of 277 oocytes were fused with cultured mammary gland cells; of these 29 reached morula/blastula stage, and were transferred into surrogate mothers leading to 13 pregnancies, but only one live birth.
Cloning is, in many situations, highly desirable since this allows
(1) indefinite multiplication of an elite desirable genotype without the risk of segregation and recombination during sexual reproduction. Obviously,
(2) the technique holds a great promise in genetic research, especially in understanding ageing and curing genetic diseases, e.g., to study the possible persistence and impact of epigenetic changes, such as, imprinting and telomere shortening, etc. In addition,

(3) this technique should make it feasible to target transgenes in livestock by nuclear transfer from transgenic cell populations developed in vitro into enucleated oocytes to recover nonchimaeric transgenic animals.
Obviously this approach would obviate the generations of breeding necessary for the recovery of transgenic animals from the chimaeric ones that are generated by embryonic stem cell transfer. The technique needs to be refined and expanded to other animals. However, in most countries, especially in all developed countries, human cloning is illegal.
 

 
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