Arm Of Metacentric Pair Research Articles

Karyotype reexamination of Corydoras paleatus (Siluriformes) and a review of the cytogenetics of genus with a focus on the ribosomal genes

The subfamily Corydoradinae is the second largest among the callictids, comprising three genera, with Corydoras Lacépède, 1803 being the largest in the number of species. The genus Corydoras has been divided into five groups of species based on differences in diploid number, chromosomal morphology, and DNA content. Chromosome studies can provide crucial details on population differentiation. To better understand the diversification that occurs in this fish group, the current study based on such markers, presents data from a population of Corydoras paleatus from the first plateau of Paraná, putting them in a comparative scenario. The specimens studied has 2n=44 chromosomes with a karyotypic formula of 18m+26sm. Although conserved, this karyotypic structure shows variation in other populations of C. paleatus already studied, a consequence of chromosomal rearrangements that modify the morphology of chromosomes without modifying the 2n, such as centromeric repositioning. C-banding revealed conspicuous pericentromeric markings in metacentric pairs 4 and 8 and in submetacentric pairs 10 and 14, whose bands have been considered a chromosomal marker not only for C. paleatus but also for the genus. Fluorescent in situ hybridization (FISH) showed the major rDNA (45S) in the terminal region of the long arm of metacentric pair 5. Such location has already been described in other populations of C. paleatus, as they have also been mapped in short arms and with multiple patterns. The present study also provides a review of the genus Corydoras regarding the 2n, karyotypic formula and mainly regarding the number and location of the 45S and 5S rDNA, confirming a scenario in which chromosomal rearrangements have been modeling karyotypes of different populations and settling in the absence of gene flow, a consequence of vicariant events that occurred in the different basins.

Skinks (Reptilia: Scincidae) Have Highly Conserved Karyotypes as Revealed by Chromosome Painting

Skinks represent the most diversified squamate reptiles with a great variation in body size and form, and are found worldwide in a variety of habitats. Their remarkable diversification has been accompanied by only a few chromosome rearrangements, resulting in highly-conservative chromosomal complements of these lizards. In this study cross-species chromosome painting using Scincus scincus (2n = 32) as the source genome, was used to detect the chromosomal rearrangements and homologies between the following skinks: Chalcides chalcides (2n = 28), C. ocellatus (2n = 28), Eumeces schneideri (2n = 32), Lepidothyris fernandi (2n = 30), Mabuya quinquetaeniata (2n = 32). The results of this study confirmed a high degree of chromosome conservation between these species. The main rearrangements in the studied skinks involve chromosomes 3, 5, 6 and 7 of S. scincus. These subtelocentric chromosomes are homologous to the p and q arms of metacentric pair 3 and 4 in C. chalcides, C. ocellatus, L. fernandi, and M. quinquetaeniata, while they are entirely conserved in E. schneideri. Other rearrangements involve S. scincus 11 in L. fernandi and M. quinquetaeniata, supporting the monophyly of Lygosominae, and one of the chromosomes S. scincus 12–16, in M. quinquetaeniata. In conclusion, our data support the monophyly of Scincidae and confirm that Scincus-Eumeces plus Chalcides do not form a monophyletic clade, suggesting that the Scincus-Eumeces clade is basal to other members of this family. This study represents the first time the whole genome of any reptile species has been used for cross-species chromosome painting to assess chromosomal evolution in this group of vertebrates.

Characterization of Aequipecten opercularis (Bivalvia: Pectinidae) chromosomes by different staining techniques and fluorescent in situ hybridization.

The chromosomes of the queen scallop Aequipecten opercularis were studied using conventional Giemsa staining, chromosome measurements, C-banding, silver staining, and fluorescent in situ hybridization (FISH) with 18S-28S rDNA and 5S rDNA probes. The karyotype (2n = 26) consists of large metacentric (pairs 1 and 2), telocentric (pairs 3, 4, 5, 6, 7, 8, and 9), and small metacentric chromosomes (pairs 10, 11, 12, and 13). The C-bands observed can be described as major and minor C-bands which are differentiated according to the intensity of the fluorescence and the frequency of the detection. Major C-bands were found on the long arm of the chromosome pairs 6, 7, 8, and 9 in an intercalary or subterminal position. Minor C-bands were located in the centromeric region in all chromosomes of the complement and also on one arm of pairs 12 and 13 in a terminal position. Silver spots were detected on the telomere of the long arms of one or two chromosomes of pair 7 in every case, although in two individuals up to four additional silver spots were detected. These were located on pairs 8 and 9 in the same position as the C-bands. 18S-28S ribosomal genes were found by FISH on the long arm of chromosome pair 7.5S ribosomal genes were located subterminally on one arm of metacentric pair 1, but two sites were differentiated in the case of elongated chromosomes. The results obtained allow for the identification of at least six different chromosome pairs in A. opercularis and contribute to the construction of an idiogram that is suitable for gene mapping and establishing accurate interspecific comparisons in scallops.