ABSTRACT
In biology, clones denote genetically identical progenies produced by a single parent. Clones are easily obtained in asexually reproducing simple organisms, plants and fungi. However, cloning does not occur in sexually reproducing higher organisms, whose progenies are drawn from equal genomic contributions from their two parents. Consequently, such progenies need not be necessarily genetically identical copies of either of the parents. In almost all higher animals, only the egg/ zygote is totipotent, i.e. the gametes have the ability to develop into a complete individual. Briefly, the unique molecular organization of egg cytoplasm alone provides the signals to the nucleus, drawn from the egg/ sperm or from a differentiated cell, to execute the programme of embryonic development. With an orderly series of divisions of the egg/ zygote, the daughter cells are progressively reduced of their original totipotency to pluripotency and finally to unipotency. The molecular organization of cytoplasm of these daughter and grand daughter cells are not capable of providing appropriate signals to their respective nuclei to execute the orchestrated programme that regulates the development of a single cell into an organized multicellular entity, i.e. while these cell nucleus have the entire genetic information, their expression is controlled by signals being received from the surrounding cytoplasm (see also Lakhotia, 2002).
