Experiences with amphibians showed that kernels of various cages of the same organism are genetically identical and in the course of a differentsirvka gradually lose ability to provide development of the reconstructed ova, however serial changes of kernels and cultivation of cages of in vitro to some extent increase this ability.
The American researchers Stik and Robl, using Salter and McGrath's method, six live rabbits received, having replaced kernels of 8-cellular of one breed in the deprived kernels of an ovum of rabbits of other breed. The phenotype been born completely corresponded to a phenotype of the donor.
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These experiences showed that normal development of mammals requires two sets of chromosomes – fatherly and maternal. Therefore at one of a known species of mammals the parthenogenesis is not described. Therefore works to Hoppa and Ilmensa did not manage to be repeated.
Work with the reconstructed ova of large pets, cows or sheep, goes a little in a different way. They are cultivated at first not by(with) in vitro, but in vivo – in the tied-up sheep yaytsevod – the intermediate (first) recipient. Then they are washed away from there and transplanted to a uterus of the final (second) recipient – cows or sheep respectively where their development happens to the developed cub. Uilandsin suggested to conclude the reconstructed ova in the agar cylinder which it transplanted then in tied up sheep or cows. According to one authors the reconstructed germs develop in a yaytsevoda, than in the cultivated environment better though some researchers received quite good results and at cultivation of in vitro.
There were also more successful works later. Uilandsin, in particular, reported that he managed to be hit four genetically identical bull-calves of holsteysky breed as a result of change in retsipiyentny ova of kernels one 32-cellular germ. The author claimed that the majority of kernels keep a totipotentnost at a 32-cellular stage, and their considerable part of a 64-cellular stage, providing normal development of the reconstructed ova to a morula stage in a yaytsevoda. After change in a uterus of cows – final recipients. As the author believes, they can normally develop further.
The success of authors of this work, first of all, is connected with use of long cellular cultures as after many passages in culture of cages the low-differentiated stem cells which it is probable could be selected and were used as donors of kernels. Of great importance was also that fact that authors, considering result of the last works, synchronized stages of a cellular cycle of ova of the recipient and ova of the donor.
Bondioli and coauthors, using 16-64-cellular germs of cows as donors of kernels, transplanted 463 reconstructed germs to a uterus of synchronized recipients, and 92 live calfs were received. Seven of them were genetically identical, representing the clone received as a result of change of kernels of cages of one donor embryo.
Why scientists so are interested in this technology? It gives the chance to receive so-called stem cells of various fabrics absolutely identical to cells of the person from whom genetic material was taken. For example, scientists can receive nervous fabric, blood, a cardiac muscle and even white and gray substance of a brain.