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4.2.8. Cloning
4.2.8. Cloning
Gene tically identical copies of certain cells and organisms are called " clones ". In vertebrates, monozygous identical twins (mammals), parthenogenetic progenies (Pisces, Amphibia, Reptilia), individuals produced by nucleus transplantation, genetically homozygous individuals etc., are all considered to be clone s. Since the various classes of vertebrates are vastly different phylogenetically, there are large number of different methods available for cloning.
Embryo splitting in mammals is a common method of producing a limited number of clones. Application of the same method to fish is however not possible today, because of the polylecithal and telolecithal type of ova.
On the other hand, there are methods of cloning applicable only in vertebrates with external embryogenesis (fish) where efficient in vitro fertilization systems exist. Production of clones by two - step gynogenesis: Meiotic and mitotic gynogenesis. Through mitotic gynogenesis 100% genetically homozygous clones are produced in common carp, zebra fish.
Cloning by a combination of andro-and gynogenesis
The production of viable diploid progeny by androgenesis is much more difficult than through gynogenesis for two reasons.
1. It is quite difficult to perform the elimination of female pronucleus and polar bodies without damaging the cytoplasm .
2. The production of diploid progeny derived from the male pronucleus is also cumbersome since there is no partner genome integrating, like the second polar body in gynogenesis. This is the reason why the first mitotic division has to be inhibited in androgenesis (endomitosis) for restoring diploidy. This second step of androgenesis cytologically corresponds to the whole of mitotic gynogenesis.
The possible genotype s produced as a result of successful diploid androgenesis are XX female and YY super male. In both cases homozygous individuals are produced, which could be used for cloning of carp. In the case of common carp female suppresses the male in growing intensity
Last modified: Thursday, 28 June 2012, 11:42 AM