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  1. PREPARED BY PRADHEES.C B.Tech.,Biotechnology
  2.  Cloning is an experimental technique wherein, a group of genetically identical organisms are produced.  Cloning of various animals has become possible due to knowledge gained in the field of developmental biology and developmental genetics.  It helped a lot, to understand the genetic control over differentiation of cells and the development of multicellular organisms.
  3.  Differentiation is an important term while considering cloning.  In the development of multicellular animals, the zygote represents the progenitor cell of the future embryo. Multitudes of cells arise from mitotic divisions of the fertilized egg cell.  These cells later become distinct cell types differing in form and function. This process is called differentiation.
  4.  Sperm cells(haploid-n) from male fertilize with the ovum(haploid-n) of female.  It results in the formation of diploid(2n) zygote.  The diploid zygote will be converted into an embryo.
  5.  Dr. Ian Wilmut has produced a cloned sheep called Dolly by nuclear transplantation method.  To produce cloned sheep he took the udder cell which is a somatic cell with diploid number of chromosomes.  An egg cell was also removed from a donor sheep.  The egg cell cannot grow into a new sheep on its own because it only has half a set of chromosomes(n).  The body cell cannot grow into a new sheep on its own because it is not a reproductive cell. So udder cell nucleus(2n) was removed.
  6.  Similarly the egg cell nucleus (n) was also removed.  The nucleus of the somatic cell (Udder) was injected into the enucleated egg.  The egg after nuclear transplantation comes to possess full set of chromosomes viz. the 2n diploid.  The egg was then transplanted back into the uterus of the sheep from which it was removed.  The egg also can be transplanted to a new surrogate mother for development.  The egg cell grew and developed into a sheep (Dolly).  This cloned sheep is genetically identical to the donor sheep which donated the diploid nucleus of its somatic cell and not the sheep which donated the egg cell.
  7.  Cloning will help to maintain biodiversity.  It can bring back even the animals which have become extinct recently and safe guard all endangered species facing extinction .  Though human cloning has its own ethical problems, the principle could be used to grow new organs from the cloned stem cells.  Such organ culture may solve transplantation problems, such as tissue incompatibility, tissue rejection, harmful immune reactions etc.  Many human lives could be saved through cloning.
  8.  When organisms are created by cloning from somatic cells of the adult, the longevity of the new born, disease tolerance capacity are some criteria to be considered.  Cloned animals have also developed diseases like arthritis. Cloned animals may have health problems. They may die at a much earlier  age than the rest of the species.  So cloned animals from somatic cells of adult, may have short life span.  cloning human may lead to the production of wrong persons.