ABSTRACT
The ribosomal cistrons of six subspecies of Bothrops neuwiedi (Serpentes) were studied at both the cytogenetic and molecular levels. These subspecies populations occur in several Brazilian regions. The analysis of the nucleolar organizing region banding patterns showed variability in the chromosomal localization of rDNA cistrons. The rDNA clusters were found in two microchromosomes, in chromosome pair Number 6, or even in the one homologue of chromosome 6, and one microchromosome, according to the specimen examined but independent of the population from which it was selected. The organization of the rDNA repeat was studied by Southern blot hybridization using Xenopus laevis ribosomal DNA probes. The size of the repeat is 10.4 kilobases (kb), and the intergenic spacer (IGS), 2.6 kb long, is relatively small compared with the size of other vertebrate IGSs. Restriction mapping using the restriction enzymes EcoRI, BamHI, HindIII, and PvuII showed a highly conserved organization of the ribosomal repeats in the total genomic DNA of the subspecies studied.
