Sinteny of ribosomal genes: evolutionary investigations on Triportheus fish species

Abstract

Ribosomal genes have been investigated in several fish species, being good chromosomal markers for the understanding of the evolutionary dynamics of the multigene repetitive families in the genome. Previous studies involving the chromosomal mapping of ribosomal genes in Triportheus species showed that, while the 5S rDNA appears more conserved in respect to its distribution, a great variation in the number and position of the 18 rDNA sites could be observed. Moreover, double-FISH analysis using both ribosomal genes, so far conducted only in T. nematurus, showed the adjacent localization of these genes on the same chromosome pair, which is an unusual feature among fish, where the distribution of such genes on different chromosome pairs is more frequent. However, it is possible that this feature is also shared by other Triportheus species, and it may be a synapomorphy for this group, as proposed for the ZZ/ZW sex chromosomes system, which is characteristic for this genus among the Characidae. Therefore, the present project aims to analyze the chromosomal distribution of 18S and 5S ribosomal genes in Triportheus species, using the double-FISH technique, verifying the presence of this sinteny in the investigated species and the relationship with respect to their location in the genome, thus adding new evidence about the evolutionary process of this group.(AU)