Chromosomal localization of 5S and 18S rRNA genes in three Parodon species (Pisces, Parodontidae)

Abstract

The nucleolar organizer regions (NORs) have often been analyzed in Parodontidae fish using silver staining. In the genus Parodon, the Ag-NORs are used as species chromosomal markers, while in the genus Apareiodon they show a more conserved location. In the present study, the NORs are investigated in three Parodon species (P. hilarii, Parodon sp. and P. tortuosus) using silver and fluorochrome staining and fluorescence in situ hybridization (FISH) with a PCRobtained 18S probe. In addition, the chromosomal 5S rDNA sites are also analyzed with a cloned 5S rDNA probe. It was seen a close correspondence between Ag-NORs, chromomycin positive regions and the 18S rDNA sites in the chromosomes of the three species. A major and a minor 5S rDNA cluster were also abserved in these species. While the 18S and major 5S rRNA genes are located on different chromosome pairs in Parodon sp. and P. hilarii, they are linked in P. tortuosus, although in opposite regions of the chromosome. Both 18S and 5S rDNA sites appear as important chromosome markers for Parodon species. © 2001 Taylor & Francis Group, LLC.