Unusually high amount of inactive ribosomal DNA in the grasshopper Stauroderus scalaris.

Fluorescence in-situ hybridization (FISH) was employed to determine the chromosomal location of the ribosomal DNA cistrons in spermatocytes of two populations of the grasshopper Stauroderus scalaris. The results showed that paracentromeric C-bands, which in this species constitute about 50% of the total chromatin, contain substantial amounts of rDNA in all chromosomes. However, silver impregnation showed the presence of a single active nucleolus organizing region (NOR) in chromosome 3 of primary spermatocytes, indicating an extremely high amount of silent rDNA across the whole genome of this species in the two geographically distant populations analysed. The significance of such an unusual phenomenon is discussed.