Metacentric Chromosomes Research Articles

Karyotype analysis of Piptanthus concolor based on FISH with a oligonucleotides for rDNA 5S

Abstract The karyotype of Piptanthus concolor was analysed via fluorescence in situ hybridization (FISH) using oligonucleotide probe for ribosomal DNA (rDNA) (5S rDNA, 41 bp). P. concolor had 2n = 18 chromosomes. The karyotype was composed of 3 pairs of metacentric chromosomes (including one pair of satellites), 3 pairs of submetacentric chromosomes, and 3 pairs of subtelocentric chromosomes. 5S rDNA loci were detected in 8 chromosome pairs. The density and location of signals for both 5S rDNA varied among individual chromosomes. High-intensity 5S signals were detected in the short arms of chromosomes 7 and 8, and weak signals were also detected in the long arms of the same chromosomes. For the satellite chromosomes, 17 and 18, the 5S rDNA signal was located at the end of the long arm. The third pair of chromosomes, 9 and 10, also significantly differed from other chromosomes with respect to the 5S rDNA signals observed in the subterminal region. The fourth pair of chromosomes, 11 and 12, had no 5S rDNA signal. The other pairs of chromosomes also exhibited individual signals. Our results provide information that may be beneficial for future cytogenetic studies and could contribute to the physical assembly of the Piptanthus genome.

New cytological data in Ophrys sect. Pseudophrys Godfery and comparative karyomorphological studies in Ophrys L. (Orchidaceae)

Eight species of Ophrys sect. Pseudophrys (Orchidaceae) were cytogenetically studied. The analysed species possess the most symmetrical karyotypes of the genus (MCA ranged from 10.21 to 15.87 and CVCL from 19.61 to 23.93) with 2n = 2x = 36, being composed of mainly metacentric chromosomes. The karyotype formulae were: 36m for Ophrys archimedea, 32m + 4sm for O. flammeola, 32m + 4sm for O. funerea, 36m for O. laurensis, 36m for O. lojaconoi, 34m + 2sm for O. lucifera, 34m + 2sm for O. obaesa and 36m for O. pallida. Karyotype morphometric characters were evaluated by calculating MCA and CVCL for the assessment of karyotype asymmetry, and CVCI for the evaluation of heterogeneity in the position of the centromeres. The relationships between species were thus finally elucidated. The species characterised by wide distribution show greater karyomorphological distance than those with restricted distribution. The possible evolutionary role of chromosomal rearrangements as well as gene mutations in the speciation of Ophrys is discussed.

Distinct classical and molecular cytogenetics of Astyanax marionae and A. fasciatus (Characiformes: Characidae): a comparative study of the organization of heterochromatin and repetitive genes.

Genus Astyanax is well distributed in Neotropical freshwater environments and its taxonomic position is uncertain, as is the case with other Characidae genera allocated in the group incertae sedis. This study aimed to analyse the karyotype of different populations of Astyanax fasciatus (Corumbataí River basin) using Giemsa staining, C-band technique, and fluorescence in situ hybridization for the H3 histone and 5S rRNA genes, in addition we describe for the first time the chromosomal organization of H3 histone and 5S rRNAgenes in A. marionae (ParaguayRiver basin). Chromosomes of three A. fasciatus populations were analysed (two with 2n = 50 and one with 2n = 48) and the heterochromatin was organized in two forms (blocks with blurred boundaries and distinct blocks). H3 histone and 5S rRNA genes were observed in all the three populations of A. fasciatus on two chromosome pairs (one metacentric chromosome showing H3 histone and 5S rRNA gene clusters). In A. marionae (2n = 48), H3 histone and 5S rRNA genes were observed in one acrocentric chromosome pair (different pairs). Further, differences between karyotypes and heterochromatin, as well as the chromosomal organization of H3 histone and 5S rRNA genes in Astyanax species, focussing on chromosome evolution in the group are discussed.

New insights into the karyotype evolution of the free-living flatworm Macrostomum lignano (Platyhelminthes, Turbellaria)

The free-living flatworm Macrostomum lignano is a model organism for evolutionary and developmental biology studies. Recently, an unusual karyotypic diversity was revealed in this species. Specifically, worms are either ‘normal’ 2n = 8, or they are aneuploid with one or two additional large chromosome(s) (i.e. 2n = 9 or 2n = 10, respectively). Aneuploid worms did not show visible behavioral or morphological abnormalities and were successful in reproduction. In this study, we generated microdissected DNA probes from chromosome 1 (further called MLI1), chromosome 2 (MLI2), and a pair of similar-sized smaller chromosomes (MLI3, MLI4). FISH using these probes revealed that MLI1 consists of contiguous regions homologous to MLI2-MLI4, suggesting that MLI1 arose due to the whole genome duplication and subsequent fusion of one full chromosome set into one large metacentric chromosome. Therefore, one presumably full haploid genome was packed into MLI1, leading to hidden tetraploidy in the M. lignano genome. The study of Macrostomum sp. 8 — a sibling species of M. lignano — revealed that it usually has one additional pair of large chromosomes (2n = 10) showing a high homology to MLI1, thus suggesting hidden hexaploidy in its genome. Possible evolutionary scenarios for the emergence of the M. lignano and Macrostomum sp. 8 genomes are discussed.

Karyological evidence of hybridogenesis in Greenlings (Teleostei: Hexagrammidae).

Two types of natural hybrids were discovered in populations of three Hexagrammos species (Teleostei: Hexagrammidae) distributed off the southern coast of Hokkaido in the North Pacific Ocean. Both hybrids reproduce by hybridogenesis, in which the maternal haploid genome is transmitted to offspring without recombination and the paternal haploid genome is eliminated during gametogenesis. While natural hybrids are unisexual and reproduce hemiclonally by backcrossing with the paternal species (BC-P), artificial F1-hybrids between the pure species produce recombinant gametes. Thus, despite having the same genome composition, the natural hybrids and the F1-hybrids are not genetically identical. Here, to clarify the differences between both hybrids, we examined the karyotypes of the three Hexagrammos species, their natural hybrids, the artificial F1-hybrids, and several backcrosses. Artificial F1-hybrids have karyotypes and chromosome numbers that are intermediate between those of the parental species. Conversely, the natural hybrids differed from F1-hybrids by having several large metacentric chromosomes and microchromosomes. Since the entire maternal haploid genome is inherited by the natural hybrids, maternal backcrosses (BC-M) between natural hybrids and males of the maternal species (H. octogrammus; Hoc) have a hemiclonal Hoc genome with large chromosomes from the mother and a normal Hoc genome from the father. However, the large chromosomes disappear in offspring of BC-M, probably due to fissuring during gametogenesis. Similarly, microsatellite DNA analysis revealed that chromosomes of BC-M undergo recombination. These findings suggest that genetic factors associated with hemiclonal reproduction may be located on the large metacentric chromosomes of natural hybrids.

Karyotype and Fluorescence In Situ Hybridization Analysis of 15 Lilium Species from China

Karyotype comparison and fluorescence in situ hybridization (FISH) were conducted to analyze the wild Lilium species distributed in China. The karyotype results revealed that all species except Lilium lancifolium (2n = 3X = 36) were diploid and had two pairs of metacentric or submetacentric chromosomes. The karyotypes of all species are similar. FISH analysis revealed that there are 5–12 45S rRNA gene loci dispersed on the chromosomes of the 14 diploid species, and 15 45S rRNA gene loci were detected in the triploid species L. lancifolium. Most of the FISH signals were detected on the long arms and the centromeric regions. Three samples of L. brownii [Hubei, China (lat. 31°28′N, long. 110°23′E); Liaoning, China (lat. 40°07′N, long. 124°19′E); and Guangxi, China (lat. 25°06′N, long. 107°27′E)] showed very similar chromosome patterns in both the karyotype and the FISH analyses, further demonstrating that these samples belonged to the same species. L. brownii is widely distributed in China from latitude 25°06′N to 40°07′N, indicating that it is highly adaptable to the environment.

Extensive Sex Chromosome Polymorphism of Microtus thomasi/Microtus atticus Species Complex Associated with Cryptic Chromosomal Rearrangements and Independent Accumulation of Heterochromatin

The sibling species Microtus thomasi and M. atticus represent probably the highest karyotypic diversity within the genus Microtus and are an interesting model for chromosomal evolution studies. In addition to variation in autosomes, they show a high intraspecific variation in the size and morphology of both sex chromosomes. We analyzed individuals with different sex chromosome constitutions using 3 painting probes, 2 from Y chromosome variants and 1 from the small arm of the submetacentric X chromosome. Our comparative painting approach uncovered 12 variants of Y and 14 variants of X chromosomes, which demonstrates that the polymorphism of sex chromosomes is substantially larger than previously reported. We suggest that 2 main processes are responsible for this sex chromosome polymorphism: change of morphology from acrocentric to submetacentric or metacentric chromosomes and increase in size due to accumulation of repetitive DNA sequences, generating heterochromatic blocks. Strong genetic drift in small and fragmented populations of these 2 species could be related to the origin and maintenance of the large polymorphism of sex chromosomes. We proposed that a similar polymorphism variation combined with random drift fixing the biggest sex chromosomes could have occurred in the origin of some of the actual Microtus species with giant sex chromosomes.

Karyomorphology and nuclear DNA content of sixteen Ophrys L. taxa from Turkey

Karyotypes in 16 representative taxa of the Ophrys genus are compared, based on Feulgen-stained somatic metaphase chromosomes. The karyotypes of O. omegaifera subsp. israelitica, O. ulupinara, O. lycia, O. argolica subsp. lucis, O. argolica subsp. lesbis, O. climacis and O. reinholdii subsp. reinholdii are described for the first time. Karyological analyses indicate relationships among the species with respect to their asymmetry indices. All Ophrys taxa studied were diploid with 2n = 2x = 36 chromosomes. One B chromosome has been detected among the chromosomes of O. argolica subsp. lucis. All karyotypes are symmetrical, consisting of metacentric and submetacentric chromosomes. The longest chromosomes of all the investigated specimens contain a secondary constriction. It is determined that there is a correlation between the total number of chromosomes having secondary constrictions and the evolutionary development order of the taxa. Based on nuclear DNA content, analysis was carried out by flow cytometer using propodium iodide as fluorochrome, 2C nuclear DNA content of 16 Ophrys species varying between 20.80 pg (O. argolica subsp. lucis) and 23.11 pg (O. omegaifera subsp. israelitica). Karyotype asymmetry relationships are discussed according to the bidimensional scatter plots of A1–A2, CVCL–CVCI, CVCL–MCA and CVCI–MCA.

Chromosomal similarity between two species ofApteronotus albifronscomplex (Apteronotidae–Gymnotiformes) implications in cytotaxonomy and karyotypic evolution

AbstractApteronotidae is one of the oldest families from the order Gymnotiformes, and is composed of 94 species that can be found from Panama to northern Argentina. Some groups such as Apteronotus present taxonomic problems, mainly related to interspecific morphological similarity. In the present study, two species belonging to Apteronotus albifrons complex from different hydrographic basins were cytogenetically analyzed in order to define chromosomal structure and propose evolutionary trends for the group. Apteronotus albifrons presented 2n = 24 (14 m + 2sm + 8a) FN = 40 and Apteronotus caudimaculosus 2n = 24 (12 m + 2sm + 10a) FN = 38; this difference in karyotypic formulae can be explained by pericentric inversion involving metacentric and acrocentric chromosomes. The karyotypic similarity between these two species indicates a chromosomal diversification, characterized by changes in karyotype formulae, which were considered an excellent cytotaxonomic marker to discriminate A. caudimaculosus of other po...

Molecular cytogenetic differentiation of paralogs of Hox paralogs in duplicated and re-diploidized genome of the North American paddlefish (Polyodon spathula)

BackgroundAcipenseriformes is a basal lineage of ray-finned fishes and comprise 27 extant species of sturgeons and paddlefishes. They are characterized by several specific genomic features as broad ploidy variation, high chromosome numbers, presence of numerous microchromosomes and propensity to interspecific hybridization. The presumed palaeotetraploidy of the American paddlefish was recently validated by molecular phylogeny and Hox genes analyses. A whole genome duplication in the paddlefish lineage was estimated at approximately 42 Mya and was found to be independent from several genome duplications evidenced in its sister lineage, i.e. sturgeons. We tested the ploidy status of available chromosomal markers after the expected rediploidization. Further we tested, whether paralogs of Hox gene clusters originated from this paddlefish specific genome duplication are cytogenetically distinguishable.ResultsWe found that both paralogs HoxA alpha and beta were distinguishable without any overlapping of the hybridization signal - each on one pair of large metacentric chromosomes. Of the HoxD, only the beta paralog was unequivocally identified, whereas the alpha paralog did not work and yielded only an inconclusive diffuse signal. Chromosomal markers on three diverse ploidy levels reflecting different stages of rediploidization were identified: quadruplets retaining their ancestral tetraploid condition, semi-quadruplets still reflecting the ancestral tetraploidy with clear signs of advanced rediploidization, doublets were diploidized with ancestral tetraploidy already blurred. Also some of the available microsatellite data exhibited diploid allelic band patterns at their loci whereas another locus showed more than two alleles.ConclusionsOur exhaustive staining of paddlefish chromosomes combined with cytogenetic mapping of ribosomal genes and Hox paralogs and with microsatellite data, brings a closer look at results of the process of rediploidization in the course of paddlefish genome evolution. We show a partial rediploidization represented by a complex mosaic structure comparable with segmental paleotetraploidy revealed in sturgeons (Acipenseridae). Sturgeons and paddlefishes with their high propensity for whole genome duplication thus offer suitable animal model systems to further explore evolutionary processes that were shaping the early evolution of all vertebrates.

Morphology, anatomy and karyology of endangered Turkish endemic Physoptychis haussknechtii Bornm. (Brassicaceae) from Central Anatolia

Abstract In this study, the morphology, anatomy, pollen morphology, leaf and seed micromorphology and karyology of the Turkish endangered endemic Physoptychis haussknechtii were investigated in detail for the first time. The species was studied in terms of detailed morphology. Basal leaves are narrowly spatulate and cauline leaves are linear to oblanceolate; both leaves are covered with flattened stalked five-armed trichomes. Raceme length was found to be up to 6 cm and 9 cm in the flowering and fruiting stages, respectively. Sepals are linear-oblong, rarely elliptic with obtuse to subacute apex. Petals are spatulate with emarginate apex. Some morphological characteristics such as dimensions of cauline leaves and ovary and length of pistil were measured for the first time. In an anatomical study, root, stem, basal leaf and cauline leaf were examined. The anatomical results showed that the plants have secondary growth in roots, primary growth in stems, amphistomatic and equifacial basal and cauline leaves with anisocytic stomata. Pollen grains are radial symmetrical, isopolar and tricolpate. The ratio of polar axis to equatorial diameter is 1.16, and pollen shape is subprolate. Exine sculpturing is reticulate under light microscope and scanning electron microscope. Seeds are obovatesuborbicular, compressed and pale brown. The chromosome number of P. haussknechtii was defined to be 2n=16. The karyotype formula of P. haussknechtii consists of five metacentric chromosome pairs and three submetacentric chromosome pairs.

Variation in genome size and karyotype among closely related aphid parasitoids (Hymenoptera, Aphelinidae).

Genome sizes were measured and determined for the karyotypes of nine species of aphid parasitoids in the genus Aphelinus Dalman,1820. Large differences in genome size and karyotype were found between Aphelinus species, which is surprising given the similarity in their morphology and life history. Genome sizes estimated from flow cytometry were larger for species in the Aphelinus mali (Haldeman, 1851) complex than those for the species in the Aphelinus daucicola Kurdjumov, 1913 and Aphelinus varipes (Förster,1841) complexes. Haploid karyotypes of the Aphelinus daucicola and Aphelinus mali complexes comprised five metacentric chromosomes of similar size, whereas those of the Aphelinus varipes complex had four chromosomes, including a larger and a smaller metacentric chromosome and two small acrocentric chromosomes or a large metacentric and three smaller acrocentric chromosomes. Total lengths of female haploid chromosome sets correlated with genome sizes estimated from flow cytometry. Phylogenetic analysis of karyotypic variation revealed a chromosomal fusion together with pericentric inversions in the common ancestor of the Aphelinus varipes complex and further pericentric inversions in the clade comprising Aphelinus kurdjumovi Mercet, 1930 and Aphelinus hordei Kurdjumov, 1913. Fluorescence in situ hybridization with a 28S ribosomal DNA probe revealed a single site on chromosomes of the haploid karyotype of Aphelinus coreae Hopper & Woolley, 2012. The differences in genome size and total chromosome length between species complexes matched the phylogenetic divergence between them.

A SNP Based Linkage Map of the Arctic Charr (Salvelinus alpinus) Genome Provides Insights into the Diploidization Process After Whole Genome Duplication.

Diploidization, which follows whole genome duplication events, does not occur evenly across the genome. In salmonid fishes, certain pairs of homeologous chromosomes preserve tetraploid loci in higher frequencies toward the telomeres due to residual tetrasomic inheritance. Research suggests this occurs only in homeologous pairs where one chromosome arm has undergone a fusion event. We present a linkage map for Arctic charr (Salvelinus alpinus), a salmonid species with relatively fewer chromosome fusions. Genotype by sequencing identified 19,418 SNPs, and a linkage map consisting of 4508 markers was constructed from a subset of high quality SNPs and microsatellite markers that were used to anchor the new map to previous versions. Both male- and female-specific linkage maps contained the expected number of 39 linkage groups. The chromosome type associated with each linkage group was determined, and 10 stable metacentric chromosomes were identified, along with a chromosome polymorphism involving the sex chromosome AC04. Two instances of a weak form of pseudolinkage were detected in the telomeric regions of homeologous chromosome arms in both female and male linkage maps. Chromosome arm homologies within the Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) genomes were determined. Paralogous sequence variants (PSVs) were identified, and their comparative BLASTn hit locations showed that duplicate markers exist in higher numbers on seven pairs of homeologous arms, previously identified as preserving tetrasomy in salmonid species. Homeologous arm pairs where neither arm has been part of a fusion event in Arctic charr had fewer PSVs, suggesting faster diploidization rates in these regions.

Fragile sites, dysfunctional telomere and chromosome fusions: What is 5S rDNA role?

Repetitive DNA regions are known as fragile chromosomal sites which present a high flexibility and low stability. Our focus was characterize fragile sites in 5S rDNA regions. The Ancistrus sp. species shows a diploid number of 50 and an indicative Robertsonian fusion at chromosomal pair 1. Two sequences of 5S rDNA were identified: 5S.1 rDNA and 5S.2 rDNA. The first sequence gathers the necessary structures to gene expression and shows a functional secondary structure prediction. Otherwise, the 5S.2 rDNA sequence does not contain the upstream sequences that are required to expression, furthermore its structure prediction reveals a nonfunctional ribosomal RNA. The chromosomal mapping revealed several 5S.1 and 5S.2 rDNA clusters. In addition, the 5S.2 rDNA clusters were found in acrocentric and metacentric chromosomes proximal regions. The pair 1 5S.2 rDNA cluster is co-located with interstitial telomeric sites (ITS). Our results indicate that its clusters are hotspots to chromosomal breaks. During the meiotic prophase bouquet arrangement, double strand breaks (DSBs) at proximal 5S.2 rDNA of acrocentric chromosomes could lead to homologous and non-homologous repair mechanisms as Robertsonian fusions. Still, ITS sites provides chromosomal instability, resulting in telomeric recombination via TRF2 shelterin protein and a series of breakage-fusion-bridge cycles. Our proposal is that 5S rDNA derived sequences, act as chromosomal fragile sites in association with some chromosomal rearrangements of Loricariidae.

Fagopyrum longzhoushanense, a new species of Polygonaceae from Sichuan, China

Fagopyrum longzhoushanense (Polygonaceae) is here described and illustrated as a new species from Longzhoushan (Puge County, Sichuan Province, China) on the basis of morphological, caryological and molecular analyses. The new species is morphologically similar to F. gracilipes from which it differs in having densely pubescent or villose parts, thicker and red-brown stems and branches, dense nodes, rugulose and small postulate leaf blade on the surface, stamens longer than pistils. Another similar species is F. densovillosum from which F. longzhoushanense differs by the winged and greater achenes, and the stamens which are longer than the pistils. From the caryioogical point of view F. longzhoushanense is a diploid species with 2n=2x=16 and a karyotype of 16 metacentric chromosomes, while F. gracilipes is tetraploid, 4n=4x=32, with a karyotype of 30 metacentric and 2 submetacentric chromosomes. The results of molecular marker analysis (matK) also highlight the distinction of the new species.

Differentiation of Nolana and Sclerophylax (Solanaceae) by means of heterochromatin and rDNA patterns

ABSTRACTWithin Solanaceae, Nolana L. f. and Sclerophylax Miers are two genera that have deserved special attention because of their rare anatomical characteristics. However, they are poorly known from the cytogenetic perspective. In order to discuss their chromosome features in an evolutionary context, classical staining, chromomycin A3/4′-6-diamidino-2-phenylindole (CMA/DAPI) fluorescent banding and in situ hybridisation (FISH) with probes for the 18-5.8-26S and the 5S rDNA loci were applied to root tips of germinating seeds. All the species presented the chromosome number 2n = 24. Karyotypes were highly symmetric, with most chromosomes being metacentric and with a maximum of three submetacentric pairs in N. divaricata. The CMA/DAPI banding technique, assayed for the first time in Sclerophylax, showed CMA+/DAPI− bands associated with nucleolar organiser regions (NORs) in the first metacentric chromosome pair in each species. The FISH technique (applied to four species of Sclerophylax and, for the first time, in one species of Nolana) showed that the 18-5.8-26S loci coincide with CMA+/DAPI− bands. Three Sclerophylax species presented two pairs of 5S signals, whereas S. adnatifolia showed three. The rDNA loci resulted as asyntenic in Sclerophylax, but were localised in the same chromosome in N. divaricata. Despite the morphological peculiarities of Nolana and Sclerophylax, the chromosome number and karyotype features are consistent with the position of the two genera within the ‘x = 12 clade’, while the number and position of rDNA loci established the chromosome rearrangements, suggesting different evolutionary pathways with respect to their closest relatives, Lycium and Jaborosa.

Cytogenetic Characterization of Species and Hybrids of Orchids of <i>Cattleya</i> Genus

This paper aims to study the cytogenetic characterization of Cattleya nobilior species and C. bowringiana and hybrids of orchids C. violacea “type”×C. granulosa, C. violacea “type”×C. harrisoniae “perola,” and C. violacea “type”×C. nobilior “amaliae.” Cattleya nobilior has 2n=2x=30 metacentric chromosomes, with size ranging from 0.54 to 1.58 µm and an active NOR in the first chromosome pair, and C. bowringiana has 2n=2x=34 metacentric chromosomes, from 0.38 to 1.46 µm of size and an active NOR in the first chromosome pair. As for the hybrids, C. violacea “type”×C. harrisoniae “pérola” has 2n=2x=32 metacentric chromosomes, with size from 0.47 to 1.73 µm and an active NOR in the second chromosome pair, C. violacea “type”×C. nobilior “amaliae” has 2n=2x=66 metacentric chromosomes, with size between 0.22 to 1.48 µm and active NORs in chromosome pairs 1 and 3, and C. violacea “type”×C. granulosa with 2n=2x=86 metacentric chromosomes, with size from 0.26 to 1.56 µm and an active NOR in chromosome pairs 3 and 23.

Karyotype and Stomatal Studies on Three Genotypes of <i>Morus</i> spp.

Three mulberry genotypes viz., MR2, C763 and Morus macroura were analyzed for the stomatal frequency and karyotypic attributes. MR2 and C763 were found to be diploids with somatic chromosome number of 2n=28, while variety Morus cathyana revealed tetraploid chromosome number of 2n=56. Somatic chromosomes measured 1.26 to 2.86µm in length. Karyotypes of these taxa are symmetric. Only metacentric and sub-metacentric chromosomes are found in the complement. Stomatal frequency was found to be high in diploid mulberry varieties compared to tetraploid variety. © 2017 The Japan Mendel Society.

First Chromosome Characterization of the Indian Giant Flying Squirrel (<i>Petaurista philippensis</i>) and Lesser Giant Flying Squirrel (<i>Petaurista elegans</i>)

We report the first chromosome analysis of the Indian giant flying squirrel (Petaurista philippensis) and lesser giant flying squirrel (P. elegans) from Northeast of Thailand. Blood samples were taken from one female squirrel. After standard whole blood lymphocytes had been cultured at 37°C for 72 h in the presence of colchicine, metaphase spreads were performed on microscopic slides and air-dried. Giemsa’s staining, GTG-banding, high resolutions GTG-banding, and CBG-banding techniques were used to stain chromosomes. The results showed that the diploid chromosome number of P. philippensis and P. elegans were 2n=38 and the fundamental numbers (NF) were 76 in both species. The chromosomes presences of metacentric and submetacentric chromosomes were 12–26 and 8–28, respectively. The largest submetacentric chromosome pair 1 showed clearly observable difference size (heteromorphic, 1a1b) in both species. GTG-banding and high-resolution GTG-banding techniques showed that number of bands of P. philippensis was 127 and 166, respectively. From the CBG-banding technique of P. philippensis showed C-positive (dark band) on the centromere of all chromosomes. Moreover, we also found dark bands on telomere of the short arm of chromosome pairs 1a, 4, 6, 7 and 9. In addition, the long arm of chromosome pair 17 showed clearly observable interstitial nucleolar organizer regions (NORs). This is the first report on polymorphism of NORs in P. elegans. The result showed that a heteromorphic had a different size of NORs of chromosome pair 17 (17a17b). The karyotype formulae could be deduced as:

The karyotype of the great sculpin, Myoxocephalus polyacanthocephalus (Pallas, 1814) (Pisces: Cottidae), from the Russian part of the species range

The karyotype of the great sculpin, Myoxocephalus polyacanthocephalus (Pallas, 1814) (Pisces: Cottidae) from the Sea of Okhotsk and the Sea of Japan has been studied for the first time. The karyotype is stable; it consists of 40 chromosomes (4 metacentric, 2 submeta-subtelocentric, 20 subtelocentric, and 14 acrocentric chromosomes); the number of chromosomal arms is 44 + 2. Nucleolar organizer regions (NOR) are found in the telomeric region of the arm in one homologue of a pair of small metacentric chromosomes, using the Ag-NOR banding technique. A comparative analysis of the karyotype of M. polyacanthocephalus and the karyotypes of other Myoxocephalus species (M. stelleri, M. brandtii, M. jaok, M. ochotensis, and M. scorpius) has been carried out based on the main karyotype characters, as well as on the number and localization of NORs. The identified differences make it possible to differentiate the studied species, whereas the general traits indicate their taxonomic proximity.