THE COMPARATIVE-ANALYSIS OF NOR POLYMORPHISM DETECTED BY FISH AND AG-STAINING ON HORSE CHROMOSOMES

The nucleolus organizer regions were investigated by FISH with biotiny lated rDNA probe and silver staining on chromosomes of the domestic ho rse (Equus caballus). Ribosomal RNA loci were mapped at the secondary constrictions of the short arm of chromosome 1 and at the pericentrome ric regions of chromosomes 27, 28 and 31. A new nucleolus-organizing c hromosome 27 was identified. The interindividual, and interchromosomal polymorphism of NORs was described in 26 horses from 5 breeds. The re lative rRNA gene activity was evaluated by the number of silver-staine d chromosomes, and the size of silver deposits. The relative amount of rDNA in NORs was estimated by intensity of fluorescent hybridization signals. The size of silver deposits and intensity of fluorescence aft er FISH were determined for each NOR using arbitrary scales of 0-3 and 0-5, respectively. The statistical analysis of these data revealed a tendency for differentiation of NOR-bearing chromosome pairs by the rR NA gene number of copies, and the activity. A close correlation betwee n activity of the rRNA genes and the relative number of rRNA gene copi es was not found for NORs of homologous chromosomes.