In the thesis theoretical generalization and new solution of an actual problem - defining patterns of ionizing radiation exposure realization on hereditary structures of human somatic cells during different terms following the Chornobyl accident - are represented, and the cytogenetic criteria to form the "risk groups" among the people, with chromosome instability, basing on improved approaches to detecting delayed, transmissible and hidden genome instability, are grounded. Individual and mid-group frequencies of cytogenetic parameters, integral and specific for the of ionizing radiation exposure, in the priority groups of Chornobyl accident victims - reconvalescents of acute radiation sickness (ARS), direct participants of the clean-up of the Chernobyl accident, children living in areas contaminated by radionuclides and workers from alienation zone and regions of obligatory evacuation - during different terms after the irradiation have been determined in comparison. In order to make analysis of different forms of chromosome instability (delayed, transmissible, hidden), new approaches have been suggested and corresponding model systems, allowing to estimate the "untargeted" cytogenetic effects long after the irradiation, which are suggested to be the cytogenetic criteria for genome stability estimation, have been devised. Basing on cytogenetic criteria, different forms of genome instability in peripheral blood lymphocytes of persons, exposed to ionizing radiation because of Chornobyl accident in dosage range between 40 and 3400 mGy long after the irradiation, have been defined. The modifying impact of ionizing radiation of wide dosage range on genetically determined human individual sensitivity to mutagens have been investigated. New molecular-cytogenetic method FISH-WCP, aimed at calculating the individual absorbed radiation doses and formation of critical groups of persons possibly having the radiation-induced pathology, has been adapted and applied. During the dynamic cytogenetic examination of persons, suffered from ARS caused by Chornobyl accident, and children, lived in areas contaminated by radionuclides, peculiarities of radiation-induced somatic chromosome mutagenesis circuit in human's body during different terms following the irradiation have been determined.
