Characterization and physical mapping of 18S and 5S ribosomal genes in Indian major carps (Pisces, Cyprinidae)

• We characterized IMCs using FISH and sequences analyses of 18S and 5S rDNAs.
• Diploid chromosome number was 50 with inter-species karyo-morphological variations.
• 18S and 5S rDNAs were ~1805bp and 191bp long fragments, respectively.
• 18S signals present on 3 pairs in catla, rohu and 2 pairs in mrigala and 5S on 1 pair.
• Results may be utilized in taxonomic identification and genetic diversity assessment.

Characterization of the major (18S) and minor (5S) ribosomal RNA genes were carried out in three commercially important Indian major carp (IMC) species, viz. Catla catla, Labeo rohita and Cirrhinus mrigala along with their physical localizations using dual colour fluorescence in situ hybridization. The diploid chromosome number in the above carps was confirmed to be 50 with inter-species karyo-morphological variations. The 18S rDNA signals were observed on 3 pair of chromosomes in C. catla and L. rohita, and two pairs in C. mrigala. The 5S rDNA signal was found on single pair of chromosome in all the species with variation in their position on chromosomes. The sequencing of 18S rDNA generated 1804, 1805 and 1805 bp long fragments, respectively, in C. catla, L. rohita and C. mrigala with more than 98% sequence identity among them. Similarly, sequencing of 5S rDNA generated 191 bp long fragments in the three species with 100% identity in coding region and 23.2% overall variability in non-transcribed spacer region. Thus, these molecular markers could be used as species-specific markers for taxonomic identification and might help in understanding the genetic diversity, genome organization and karyotype evolution of these species.