[Interindividual and intercellular differences in the total activity of ribosomal genes detectable by the Ag staining of nucleolus organizer regions in human acrocentric chromosomes].

Selectively Ag-stained nucleolar organizing regions (NORs) of human chromosomes were analysed using four size categories: 0, 1, 2 or 3 grades. A criterion of NORs' total activity has been proposed as a sum of grades (sigma (+]. On this basis, interindividual polymorphism was defined in 60 healthy individuals with normal karyotypes. The reaction norm of sigma (+) was determined (from 16 to 22 grades). In the cells of the patients with two nucleolar organizing chromosomes involved in Robertsonian translocations the sigma (+) was within the reaction norm (16-19). The total NORs activity was determined in a patient having both normal karyotype cells and two cell clones with one or two small bisatellited chromosomes: sigma (+) in three cell clones amounted to 20.5, 23.0 and 26.3. In the clones with additional NORs, the silver staining intensity for 10 NORs of the main set did not change, which leads to a suggestion that no compensatory change in the number of rRNA gene copies working takes place in man. The data obtained allow to suppose that zygotic selection operates in man, which ensures maintainance of the number of the ribosomal gene's copies necessary for viability of an individual.