[Nucleolus organizer region activity of human chromosomes in relation to age].

Ag-stained acrocentric chromosomes were cytogenetically studied in 20 individuals aged 20-50, 80 and in older ones. It is revealed that the number of Ag-positive nucleolus regions and association frequency of Ag-stained acrocentric chromosomes statistically decreased in the individuals of old age as compared with the middle-aged persons. This is supposed to be conditioned by heterochromatinization of the satellite stalks of the 13th, 21st and 22 d chromosomes in the process of ageing.