Analysis of Genomic Equivalence of Nuclei
Towards the ending of 19th century August Weismann had proposed that during cleavage the genetic determinants (later shown to be chromosomes) were parceled out between different blastomeres in some manner that determined the path of differentiation that a given cell might take. As per to this theory only the germ cells contained all the genetic determinants and the several somatic cell types differed in the genetic determinants that they contained. In other words, the nuclei of only the germ cells consist of all the genes and have a complete genome, whereas the nuclei of dissimilar somatic cells may contain only those genes that are needed for their specific type of differentiation.
However, on the basis of many studies it is believed that in an organism nuclei of all cells of the body consist of a complete and identical set of all the genes as that in the original nucleus of the zygote. It means that the genomes of all cells and the zygote are equal. Development involves utilization of different genes from this common genome through each cell type for its own particular type, of differentiation. This belief in genomic equivalence of nuclei of all cells is supported through a fair amount of evidence of both genetic and embryological nature. It has been found that particular number of chromosomes, on which genes are arranged, is constant throughout all the dissimilar tissues of the adult organism. The DNA, the carrier of genetic information, extracted from different somatic tissues has identical composition and properties. It has been shown that in the larvae of Chironomus and as well Drosophila the number of chromosomes and their banding pattern (pointing out the number of genes) are constant in all cells.