RESUMO
To reveal functional organization of chromosome at late stages of antogenesis we observed heterochromatinization (genetically inactive regions of condensed hetero - or euchromatin) of chromosomes (electron micrographs of lymphoblasts chromatin: heat absorption of condensed chromatin: Ag-positive NORs and associations of acrocentric chromosomes: RNA transcriptional activity): mutation level (aberrations and aneuploidy) and DNA repair capacity (intensity of unscheduled DNA synthesis and sister chromatid exchanges - SCEs.) during aging (from 70 to 114 year). The results obtained permit us to infer that enhanced heterochromatinization in old age blocks reparative enzymes resulting in increased numbers of cells with chromosome mutations. We may conclude that the lowering of DNA repair and the increase of mutation frequency at aging are secondary to the progress of heterochromatinization in chromosomes (gene repression). This indicates a key role of heterochromatinization in aging process.