Localization and Characterization of the 5S rDNA Bearing Chromosome in Two Steindachneridion Species by Means of Different Cytogenetic Techniques

Abstract

Karyotype macrostructure and nucleolar organizer regions have often been studied in Neotropical siluriform fishes, but data about structural rearrangements and gene mapping are scarce. 5S rDNA is localized and characterized in Sorubiminae species (Steindachneridion melanodermatum and S. scriptum) using fluorescence in situ hybridization, C- and G-banding and restriction enzyme banding (AluI, BamHI and EcoRI). Chromosome mapping of 5S rDNA genes showed only one site located on the short arms of subtelocentric chromosome pair (chromosome 23) in both species, with no apparent polymorphisms. This region is C-positive and shows a clear G-band, having no cleavage sites for the restriction enzymes tested. These genes are not syntenical with the 18S ones and their karyotype location remains conserved in the species studied, appearing as a cytogenetic marker.