| Summary: | In vertebrate, the 5S ribosomal DNA (rDNA) consists of a conserved coding (transcriptional) unit of 120 bp (5S), which is separated from the next unit by a nontranscribed spacer (NTS). The coding sequence and the NTS together form a repeat unit which can be found in hundreds to thousands of copies tandemly repeated in the genomes. The coding region is highly conserved, even among nonrelated taxa, whereas the spacer region is variable, both in length and in sequence. Many studies have shown that birth-and-death processes can drive the evolution of 5S rDNA in distantly related taxa. The variations are due to insertions, internal subrepeats, deletions, base substitutions, pseudogenes, therefore the NTSs seem to be subject to rapid evolution. Thus, 5S rDNA sequences have been used as species – specific or population – specific genetic and cytogenetic markers in evolutionary studies: studying intraspecific variation, genome evolution, and phylogenetic reconstruction. Little is known about the nucleotide sequences and chromosomal location of 5S rDNA in teleosts in comparison with other vertebrate classes.
Our preliminary research has related to diploid individuals of gibel carp (Carassius gibelio) with 2n=100 chromosomes. The PCR reaction has resulted in product 340 bp. Sequencing has yielded data on the exact nucleotide sequence and length of 5S rDNA fragment. Studies have shown no difference in length and nucleotide composition of the 5S sequence between males and females. Some study has revealed the influence of polyploidy on the organization and evolution of the 5S rDNA in teleosts fishes, therefore, then we will have studied the 5S rDNA sequences in triploid individuals.
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