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Abstract: This paper describes a study of the 5S ribosomal RNA genes (5S rDNA) in a group of 6 species belonging to 4 genera of Mugilidae. In these 6 species, [...]

Standard karyotypes of two species of the genus Scincella, S. assata and S. cherriei, both from Chiapas State, Mexico, were described for the first time. The diploid chromosome number was 28 in S. assata, whereas 30 in S. cherriei. The karyotypes of the two species, while differing in the number of microchromosomes, 14-15 in S. assata and 16-17 in S. cherriei, share four pairs of large metacentric, two pairs of medium-sized metacentric, and one particular pair (number 7) of chromosomes. Female S. assata carries chromosome pair 7 composed of two identical medium-sized subtelocentric chromosomes. This chromosome pair is heteromorphic in males of both species, i.e., one component of the pair is similar to the homomorphic chromosomes 7 of the S. assata female, while the other is nearly one-half the size of its counterpart and resembles a microchromosome. The homology of such externally different elements is deducted from the presence of an asymmetric bivalent in spermatocytes at diplotene-diakinesis. Female S. cherriei was not available. We suspect that the two Scincella species possess an XY sex determination system, as previously reported for the North American congeneric species, S. lateralis. [ABSTRACT FROM AUTHOR]

This paper describes a study of the 5S ribosomal RNA genes (5S rDNA) in a group of 6 species belonging to 4 genera of Mugilidae. In these 6 species, the relatively short 5S rDNA repeat units, generated by PCR and ranging in size from 219 to 257 bp, show a high level of intragenomic homogeneity of both coding and spacer regions (NTS-I). Phylogenetic reconstructions based on this data set highlight the greater phylogenetic and genetic diversity of Mugil cephalus and Oedalechilus labeo compared with the genera Liza and Chelon. Comparative sequence analysis revealed significant conservation of the short 5S rDNA repeat units across Chelon and Liza. Moreover, a second size class of 5S rDNA repeat units, ranging from roughly 800 to 1100 bp, was produced in the Liza and Chelon samples. Only short 5S rDNA repeat units were found in M. cephalus and O. labeo. The sequences of the long 5S rDNA repeat units, obtained in Chelon labrosus and Liza ramada, differ owing to the presence of 2 large insertion/deletions (indels) in the spacers (NTS-II) and show considerable sequence identity with NTS-I spacers. Interspecific sequence variation of NTS-II spacers, excluding the indels, is low. Southern-blot hybridization patterns suggest an intermixed arrangement of short and long repeat units within a single chromosome locus. Cet article décrit une étude portant sur les gènes d’ARN ribosomique 5S (ADNr 5S) chez un groupe de 6 espèces appartenant à 4 genres au sein des mugilidés. Chez ces 6 espèces, les répétitions relativement courtes d’ADNr 5S, dont la taille des produits amplifiés par PCR varie entre 219 et 257 pb, présentent une grande homogénéité intragénomique tant au sein des régions codantes qu’au sein des espaceurs (NTS-I). Des reconstructions phylogénétiques sur la base de ces données mettent en relief la plus grande diversité phylogénétique et génétique chez le Mugil cephalus et l’Oedalechilus labeo par rapport aux genres Liza et Chelon. Des analyses comparées de séquences ont révélé une conservation significative des répétitions courtes d’ADNr 5S au sein des genres Chelon et Liza. De plus, une seconde classe d’ADNr 5S, dont la taille variait entre environ 800 et 1100 pb, a été observée chez les échantillons des genres Chelon et Liza. Seules des répétitions courtes ont été trouvées chez le M. cephalus et l’O. labeo. Les séquences de ces longues répétitions d’ADNr 5S, obtenues chez le Chelon labrosus et le Liza ramada, diffèrent en raison de la présence de deux grandes insertions/délétions (indels) dans les espaceurs (NTS-II) et montrent une très grande similarité avec les espaceurs NTS-I. La variation interspécifique de la séquence des espaceurs NTS-II, en dehors des indels, est faible. Les résultats d’hybridations Southern suggèrent la présence au sein d’un même locus chromosomique des répétitions courtes et longues entremêlées. [ABSTRACT FROM AUTHOR]

The European whitefish, Coregonus lavaretus, widely distributed in freshwater of northern Europe and introduced into the major lakes of northern Italy, has been restocked in central Italian lakes. In accordance with current managing practices, a reduced number of spawners contribute to reproduction within each lake and a certain degree of isolation is to be expected between populations from different lakes, resulting in the rapid fixing of chromosomal changes. A detailed survey of three populations from different lakes was carried out using classical and molecular cytogenetic techniques, to verify if specific chromosomal markers are present in the distinct populations. The comparative analysis revealed intraspecific variability of NORs and fixed differences in their number in the three populations. A co-localization of major and minor rRNA genes on one chromosome site was also observed. The original data regarding the chromosome mapping of the (TTAGGG)n telomeric repeat obtained in this study, demonstrated their exclusively terminal distribution, and a conspicuous inter-chromosomal variation in the number of repeats. The results are compared with data available for populations from native geographic ranges. [ABSTRACT FROM AUTHOR]

Three specimens of M. minutoides/musculoides from Zambia were cytogenetically studied through G- and C-banding, DAPI staining and fluorescence in-situ hybridization (FISH) with a (TTAGGG)n telomeric sequence. Biarmed chromosomes were identified according to the current nomenclature as follows: Rb(2.7), Rb(3.12), Rb(4.5), Rb(6.8), Rb(9.16), and the sex chromosomes Rb(1.X), Rb(1.Y) and Rb(1.Xd), originated from the deleted X chromosome. One female showed the diploid number 2n=24; in the two other individuals, the Rb(9.16) occurred in a heteromorphic condition, and, accordingly, the diploid number was 2n=25. FISH showed the sites of telomeric sequences at telomeres of all the chromosomes, and in an interstitial position at the centromeres of all Robertsonian metacentrics, except one – the Rb(6.8), though the patterns of hybridization varied between chromosomes. Sex chromosome pairs, in the male and females, showed a similar C-banding pattern, but revealed clear differences after FISH. Traces of telomeric sequences were found dispersed in the whole-heterochromatic arm of the Rb(1.Xd). No visible bond between C-positive heterochromatin and telomeric sequences were detected in the other either bi- or uniarmed chromosomes, indicating that they may actually represent retained telomeres in the Robertsonian metacentrics. [ABSTRACT FROM AUTHOR]

The European whitefish, Coregonus lavaretus, widely distributed in freshwater of northern Europe and introduced into the major lakes of northern Italy, has been restocked in central Italian lakes. In accordance with current managing practices, a reduced number of spawners contribute to reproduction within each lake and a certain degree of isolation is to be expected between populations from different lakes, resulting in the rapid fixing of chromosomal changes. A detailed survey of three populations from different lakes was carried out using classical and molecular cytogenetic techniques, to verify if specific chromosomal markers are present in the distinct populations. The comparative analysis revealed intraspecific variability of NORs and fixed differences in their number in the three populations. A co-localization of major and minor rRNA genes on one chromosome site was also observed. The original data regarding the chromosome mapping of the (TTAGGG)(n) telomeric repeat obtained in this study, demonstrated their exclusively terminal distribution, and a conspicuous inter-chromosomal variation in the number of repeats. The results are compared with data available for populations from native geographic ranges.