Karyotype analysis of Oreochromis mossambicus, O. urolepis hornorum and their hybrid based on Cot-1 DNA bands by fluorescence in situ hybridization

Abstract

Chromosomal karyotypes of Oreochromis mossambicus and O. urolepis hornorum and their hybrid were analysed by means of Cot-1 DNA bandings through fluorescence in situ hybridization (FISH). To identify all chromosomes, Cot-1DNA - which contains highly and moderately repetitive DNA - was extracted from genomic DNA, labelled as a probe with Dig-11-dUTP, and in situ hybridized to spreads of mitotic chromosomes of the three samples. The hybridized signals were detected by means of Cy3-conjugated antidigoxigenin. The FISH results indicated that the three samples had the same diploid number (2n = 44) of chromosomes. Specific fluorescence signal bands were detected on all individual chromosome pairs. On the basis of Cot-1 DNA FISH banding patterns and chromosome morphology, the karyotypes of the three samples have been constructed; no remarkable differences were detected between the karyotypes of these species using this method. These results - which are similar to those reported previously, with respect to chromosome number, morphology and Cot-1DNA FISH patterns - suggest chromosomal stasis during speciation and hybridization of tilapia (Oreochromis, Cichlidae). Such a molecular cytogenetic procedure, if used in conjunction with other genomic research methods, could facilitate the study of genomic structure and be adapted for chromosome studies of other animal species.