Sequential silver staining and hybridization in situ on nucleolus organizing regions in human cells

Chromosome preparations from eight individuals were first stained with silver nitrate to reveal the nucleolus organizing regions (NORs) and then hybridized in situ with ribosomal RNA. In six individuals the size of the silver-staining regions was positively correlated with the amount of label present after hybridization in situ. Thus the variation in silver-staining intensity among chromosomes was largely explained by variation in the number of rDNA gene copies per NOR. However, in two individuals this correlation was absent, suggesting that other factors can also influence the size of the silver-staining region.