The activity of nucleolar organizer regions of human chromosomes in extreme old age

Ag-positive nucleolar organizer regions (NORs) and associations of silver-stained acrocentric chromosomes were studied in 400 metaphases from 20 male and female subjects aged 20-50 and 80 or over. The number of Ag-positive NORs and the frequency of chromosome associations were found to be decreased significantly at 80 and thereafter in comparison with middle age. The use of G stain revealed a significant age-dependent decline in the numbers of argent-affine 13th and 21st chromosomes and the frequency of associations formed by the 13th and 22nd chromosomes. These phenomena seem to be determined by heterochromatinization of satellite stalks of the 13th, 21st and 22nd chromosomes during aging.