Heteromorphism of rDNA Size in Pinirampus pirinampu (Pisces : Pimelodidae) Detected by in situ Hybridization

Abstract

The ribosomal RNA genes of Pinirampus pirinampu have been localized by fluorescence in situ Hybridization hybridization (FISH) with 18S rDNA probe. This method allowed the location of FITC signals on the short arm of the biggest subtelocentric chromossomic pair and evidenced a size heteromorphism of hybridization signals between homologous chromosomes. This difference has been attributed to variation in the amount of rRNA genes per cluster, probably due structural modifications (i.e. duplications by unequal crossing over or transpositions) of NOR involving homologous segments.