[Diminution of chromatin, accompanying reorganization of genomic molecular structure: evolutionary aspects]

Chromatin diminution (CD) accompanied by the reorganization of the molecular genomic structure of macronuclei in ciliates and somatic cells in Cyclops and Ascaris is considered. A conclusion is drawn that the physical elimination of most (sometimes 94-98%) genetic material from somatic nuclei directly indicates that, in these species, eliminated sequences possess neither the coding nor the regulatory functions that are required for differentiation. Apparently, the actual functions of eliminated sequences are associated only with germline chromosomes where these sequences act as a factor of genetic isolation. A CD is supposed to be underlain by the coordinated operation of many genes. Consequently, this phenomenon cannot result from stochastic mutagenesis and the random coincidence of required mutations in several genes. For CD formation, canalized mutagenesis is required, which simultaneously generates a set of genes that code the consecutive stages of CD.