Populational polymorphisms in silver staining of nucleolus organizer regions (NORs) in human acrocentric chromosomes.

The Ag stainability of the nucleolus organizer region (NOR) was studied in the acrocentric chromosomes identified by Q banding of cultured lymphocytes in 41 karyotypically normal persons (33 males and 8 females) originating from southeast Estonia. The data obtained are compared with those established earlier for a combined Vienna-Ulm population of 51 karyotypically normal persons (see Mikelsaar et al., 1977a). Significant differences between the two populations in the frequency and patterns of Ag-positive NORs were found. The following findings were most striking: the frequency of Ag-positive NORs in chromosome 14 and in the totals was significantly lower in the Estonian population than in the Vienna-Ulm population (P less than 0.01). The average modal number of Ag-positive NORs per individual was 7.8 in the Estonian population and 8.7 in the Vienna-Ulm sample (P less than 0.01). If the data of the two populations were combined the frequency of positive NORs was significantly (P less than 0.05) lower in chromosome 22 than in 13, 15, and 21, but not 14.