Molecular Cytogenetic Analysis of the European Hake Merluccius merluccius (Merlucciidae, Gadiformes): U1 and U2 snRNA Gene Clusters Map to the Same Location

The European hake (Merluccius merluccius) is a highly valuable and intensely fished species in which a long-term alive stock has been established in captivity for aquaculture purposes. Due to their huge economic importance, genetic studies on hakes were mostly focused on phylogenetic and phylogeographic aspects; however chromosome numbers are still not described for any of the fifteen species in the genus Merluccius. In this work we report a chromosome number of 2n = 42 and a karyotype composed of three meta/submetacentric and 18 subtelo/telocentric chromosome pairs. Telomeric sequences appear exclusively at both ends of every single chromosome. Concerning rRNA genes, this species show a single 45S rDNA cluster at an intercalary location on the long arm of subtelocentric chromosome pair 12; the single 5S rDNA cluster is also intercalary to the long arm of chromosome pair 4. While U2 snRNA gene clusters map to a single subcentromeric position on chromosome pair 13, U1 snRNA gene clusters seem to appear on almost all chromosome pairs, but showing bigger clusters on pairs 5, 13, 16, 17 and 19. The brightest signals on pair 13 are coincident with the single U2 snRNA gene cluster signals. Therefore, the use of these probes allows the unequivocal identification of at least 7 of the chromosome pairs that compose the karyotype of Merluccius merluccius thus opening the way to integrate molecular genetics and cytological data on the study of the genome of this important species.Versión del editor4,411

Chromosome banding patterns of the gudgeon, Gobio gobio (Actinopterygii, Cyprinidae)

Background. The gudgeon is one of the most divergent fish species in Europe. Morphological variability related to sex, size, ecological characters, and geographical distribution are well documented in the literature. Apart from the only few data on the karyotype, chromosome banding patterns of this species have not been studied. Cytogenetic features are very useful tools in taxonomic descriptions of cyprinid species. The aim of this study was to describe and characterise the banding patterns of the gudgeon karyotype. Materials and methods. Cytogenetic examinations of 15 specimens of gudgeon from the upper part of the Odra River, Poland, were carried out. Different chromosome banding techniques: Giemsa staining, C-banding, silver nitrate, chromomycin A3 and DAPI staining were used. Results. The karyotype of gudgeon consisted of 2n = 50 chromosomes, and NF = 98 chromosome arms. Ag-NORs were located on one submeta-subtelocentric chromosome pair and the size polymorphism of NORs was detected. The chromosome sites with G-C rich DNA on one submeta-subtelocentric chromosome pair and heterochromatin block in the centromeric regions were found. Low accumulation of A-T pair rich regions were indicated by DAPI staining. Conclusion. The presently described new chromosomal features of Gobio gobio substantially enhance our knowledge on the taxonomy of this species at cytogenetic level. Jointly with data on morphological- and genetic variability they could be used to determine the phylogeny of the genus Gobio and related species