Karyotypes Of Species Research Articles

Extraordinarily conserved chromosomal synteny of Citrus species revealed by chromosome-specific painting.

Reliable identification of individual chromosomes in eukaryotic species is the foundation for comparative chromosome synteny and evolutionary studies. Unfortunately, chromosome identification has been a major challenge for plants with small chromosomes, such as the Citrus species. We developed oligonucleotide-based chromosome painting probes for all nine chromosomes in Citrus maxima (Pummelo). We were able to identify all C.maxima chromosomes in the same metaphase cells using multiple rounds of sequential fluorescence in situ hybridization with the painting probes. We conducted comparative chromosome painting analysis in six different Citrus and related species. We found that each painting probe hybridized to only a single chromosome in all other five species, suggesting that the six species have maintained a complete chromosomal synteny after more than 9million years of divergence. No interchromosomal rearrangement was identified in any species. These results support the hypothesis that karyotypes of woody species are more stable than herbaceous plants because woody plants need a longer period to fix chromosome structural variants in natural populations.

Karyotypic analyses and genomic affinity among Argentinean species of Passiflora

Abstract The genus Passiflora (Passifloraceae) has more than 500 species, nineteen are native to Argentina. By their austral distribution, these species were included in breeding programs to obtain ornamental varieties tolerant to low temperatures. The aim of this work was to know the cytogenetic characteristics of Passiflora genotypes present in a working collection, as an indispensable knowledge for the development of a breeding plan. Chromosomal preparations were performed and karyotypic characteristics, rDNA sites by FISH and affinity among subgenera by GISH were studied. Chromosome counts in fourteen Argentinean species confirmed the basic chromosome numbers previously published: x = 6 for subgenus Decaloba, x = 9 for subgenus Passiflora and x = 10 for Dysosmia. The karyotypic parameters (karyotype, haploid chromosome length and asymmetry indices) and genomic affinities among the subgenera, clarify most of the chromosomal evolution of the genus. The results obtained strongly suggest that the basic number x = 6 would be the original one and that x = 9 was originated by processes of polyploidy and descendent dysploidy. Since subgenus Passiflora possesses the largest genomes, it is postulated that evolutionary process leading to x = 9 was accompanied by unequal distribution of non-coding repetitive DNA, mainly transposable elements. These processes could explain the asymmetrical karyotypes of species of subgenus Passiflora.

Karyological, Molecular and Cytogenetical Studies on Tree Plants in V.N. Sukachev Institute of Forest

Aim. The aim of the article is to find out the karyological features and conduct molecular and cytogenetic analysis on tree plants for biological diversity studies, solve problems of taxonomics, evolutionary and population genetics. Methods. Classic methods with acetohematoxylin staining of slides and new method of fluorescent in situ hybridization (FISH) had been used. Results . More than 250 populations and provenances of representatives of different genera of gymnosperms from the families Pinaceae, Cupressaceae, Ephedraceae and tree angiosperms from the families Rosaceae, Aceraceae, Polygonaceae, Nitrariaceae, Rhamnaceae, Fabaceae, Ericaceae were studied. Investigations had been conducted in natural populations and during the introduction, in optimal and extreme conditions, in disturbed ecosystems, botanical gardens and parks; in addition, various intraspecific forms and unique trees had been studied. The variability of chromosome numbers and a wide range of chromosomal mutations had been revealed. Use of fluorescence in situ hybridization (FISH) with the 45S and 5S ribosomal RNA gene probes and DAPI staining allowed to identify of homologous chromosome pairs in the karyotypes of conifers and to facilitate the comparative karyotype analysis of those species. Analysis of the chromosome numbers of woody angiosperms showed a significant role of polyploidy in their evolution. Conclusions. The studies on karyotypes in tree species showed their diversity, variability of chromosome numbers, higher level of chromosomal anomalies and their wide spectrum in extreme conditions, under introduction and also in cultivars and abnormal form of trees. The use of molecular cytogenetic markers made it possible to obtain new information on the structure of conifer chromosomes. The role of polyploidy in the evolution of woody angiosperms was shown.

Phylogenetic relationships between genera Dorcadion, Lamia, Morimus, Herophila and some other Lamiinae (Coleoptera: Cerambycidae) based on chromosome and CO1 gene sequence comparison.

A dual molecular and cytogenetic study was performed with the aim to improve the controversial systematic classification of some species of Lamiinae (Coleoptera: Cerambycidae). The karyotypes of species belonging to genera Morimus, Herophila, Dorcadion, Neodorcadion and Lamia share a number of characters, which differentiate them from other species, belonging to genera Phytoecia, Parmena and Monochamus. The karyotypes of the last three species comprise 20 chromosomes, mostly metacentric or sub-metacentric, as in the presumed Cerambycidae ancestors. The karyotypes of the former species share many characters derived from the Lamiinae ancestors by a number of chromosome fissions and inversions indicating their monophyly. Comparisons of the CO1 gene sequence also show the monophyly of Morimus, Lamia, Herophila and Dorcadion and their distant relationship with others. These convergent results allow us to propose a phylogenetic classification of these genera, which places the monospecific genus Lamia close to Dorcadion, clearly separates Dorcadion and Neodorcadion and places Herophila closer to Morimus than to Dorcadion/Lamia. The genus Morimus is the most derived. CO1 mutations loosely separate the forms M. asper and M. funereus, which have similar karyotypes and behaviour and copulate in captivity. The form M. ganglebaueri may have a funereus X asper hybrid origin.

Molecular cytogenetics of valuable Arctic and sub-Arctic pasture grass species from the Aveneae/Poeae tribe complex (Poaceae)

BackgroundGrasslands in the Arctic tundra undergo irreversible degradation due to climatic changes and also over-exploitation and depletion of scarce resources. Comprehensive investigations of cytogenomic structures of valuable Arctic and sub-Arctic grassland species is essential for clarifying their genetic peculiarities and phylogenetic relationships, and also successful developing new forage grass cultivars with high levels of adaptation, stable productivity and longevity. We performed molecular cytogenetic characterization of insufficiently studied pasture grass species (Poaceae) from related genera representing two neighboring clades: 1) Deschampsia and Holcus; 2) Alopecurus, Arctagrostis and Beckmannia, which are the primary fodder resources in the Arctic tundra.ResultsWe constructed the integrated schematic maps of distribution of these species in the northern, central and eastern parts of Eurasia based on the currently available data as only scattered data on their occurrence is currently available. The species karyotypes were examined with the use of DAPI-banding, multicolour FISH with 35S rDNA, 5S rDNA and the (GTT)9 microsatellite motif and also sequential rapid multocolour GISH with genomic DNAs of Deschampsia sukatschewii, Deschampsia flexuosa and Holcus lanatus belonging to one of the studied clades. Cytogenomic structures of the species were specified; peculiarities and common features of their genomes were revealed. Different chromosomal rearrangements were detected in Beckmannia syzigachne, Deschampsia cespitosa and D. flexuosa; B chromosomes with distinct DAPI-bands were observed in karyotypes of D. cespitosa and H. lanatus.ConclusionsThe peculiarities of distribution patterns of the examined chromosomal markers and also presence of common homologous DNA repeats in karyotypes of the studies species allowed us to verify their relationships. The obtained unique data on distribution areas and cytogenomic structures of the valuable Arctic and sub-Arctic pasture species are important for further genetic and biotechnological studies and also plant breeding progress.

Comparatively Barcoded Chromosomes of Brachypodium Perennials Tell the Story of Their Karyotype Structure and Evolution.

The Brachypodium genus is an informative model system for studying grass karyotype organization. Previous studies of a limited number of species and reference chromosomes have not provided a comprehensive picture of the enigmatic phylogenetic relationships in the genus. Comparative chromosome barcoding, which enables the reconstruction of the evolutionary history of individual chromosomes and their segments, allowed us to infer the relationships between putative ancestral karyotypes of extinct species and extant karyotypes of current species. We used over 80 chromosome-specific BAC (bacterial artificial chromosome) clones derived from five reference chromosomes of B. distachyon as probes against the karyotypes of twelve accessions representing five diploid and polyploid Brachypodium perennials. The results showed that descending dysploidy is common in Brachypodium and occurs primarily via nested chromosome fusions. Brachypodium distachyon was rejected as a putative ancestor for allotetraploid perennials and B. stacei for B. mexicanum. We propose two alternative models of perennial polyploid evolution involving either the incorporation of a putative x = 5 ancestral karyotype with different descending dysploidy patterns compared to B. distachyon chromosomes or hybridization of two x = 9 ancestors followed by genome doubling and descending dysploidy. Details of the karyotype structure and evolution in several Brachypodium perennials are revealed for the first time.

Cytological and molecular characterization of Thinopyrum bessarabicum chromosomes and structural rearrangements introgressed in wheat

Thinopyrum bessarabicum is an important genetic resource for wheat improvement by chromosome engineering. However, the present low-resolution karyotype limits identification of its chromosomes. Oligonucleotide probes to identify tandem repeats provide an efficient way to produce high-resolution karyotypes in many species. In this study, putative tandem repeats were identified using unassembled sequence reads of Th. bessarabicum, and 306 repeat clusters were identified. Among them, 17 had conserved motifs that varied in size from 71 to 856 bp and occupied 0.01% to 1.30% of the genome. Thirty-nine oligonucleotides from 17 clusters were developed, and 21 from 8 clusters produced clear and stable signals in Th. bessarabicum chromosomes. Five tandem repeat clusters were distributed only at the telomeric or subtelomeric regions, and the BSCL242 probe produced signals only on chromosome 7JL. The other three were mainly in intercalary and centromeric regions with a few weak signals in telomeric regions. A new multiplex oligonucleotide probe (ONPM#7) containing 13 oligonucloetides distinguished all wheat and Th. bessarabicum chromosomes after one round of FISH. The high-resolution karyotype of Th. bessarabicum in corresponding with the seven homoeologous group chromosomes of wheat has been developed. Three spontaneous translocations and one isochromosome among Th. bessarabicum chromosomes introgressed into wheat thus have been characterized in combined with molecular marker analysis. The ONPM#7 probe and molecular markers provide powerful tools for engineering transfer of chromosomal segments from Th. bessarabicum to wheat.

An extraordinarily stable karyotype of the woody Populus species revealed by chromosome painting.

The karyotype represents the basic genetic make-up of a eukaryotic species. Comparative cytogenetic analysis of related species based on individually identified chromosomes has been conducted in only a few plant groups and not yet in woody plants. We have developed a complete set of 19 chromosome painting probes based on the reference genome of the model woody plant Populus trichocarpa. Using sequential fluorescence in situ hybridization we were able to identify all poplar chromosomes in the same metaphase cells, which led to the development of poplar karyotypes based on individually identified chromosomes. We demonstrate that five Populus species, belonging to five different sections within Populus, have maintained a remarkably conserved karyotype. No inter-chromosomal structural rearrangements were observed on any of the 19 chromosomes among the five species. Thus, the chromosomal synteny in Populus has been remarkably maintained after nearly 14million years of divergence. We propose that the karyotypes of woody species are more stable than those of herbaceous plants since it may take a longer period of time for woody plants to fix chromosome number or structural variants in natural populations.

Karyotype Analysis of the New Talpa Species Talpa aquitania (Talpidae; Insectivora) from Northern Spain

Karyotypes of 3 male Talpa specimens from northern Spain were analyzed. The mesostyles of upper molars and cytochrome b sequence analysis identified these specimens as belonging to Talpa aquitania, a new Talpa species recently described from northern Spain and southern France. We describe here for the first time the karyotype of Talpa aquitania. Its diploid number is 2n = 34 and NFa = 64, and all chromosomes including the sex chromosomes are biarmed, either metacentric or submetacentric. G-banding demonstrated that the karyotypes of T. aquitania and T. occidentalis (the most closely related species) are almost identical. However, the karyotype of T. aquitania differs from the karyotypes of both T. europaea and T. occidentalis in that it has a medium-sized biarmed Y chromosome rather than a dot-like chromosome and that chromosome 16 is submetacentric in T. aquitania but has a small p-arm in both T. europaea and T. occidentalis. Pericentromeric C-bands were scarce and only clearly visible in a few chromosomal pairs. In addition, C-banding demonstrated that half of the 14p, the 16p, and the Y chromosome are all heterochromatic. rDNA genes were located at the secondary constriction in autosomal pair 3, a common feature in the karyotypes of all Talpa species. Hybridization signals for telomeric repeats were found on the telomeres and the pericentric regions of some chromosomes and co-localized in the secondary constriction of pair 3 with the rDNA genes. In conclusion, the karyotype of T. aquitania from northern Spain is very similar to the karyotype of other species belonging to the genus Talpa.

A chromosome-anchored eggplant genome sequence reveals key events in Solanaceae evolution

With approximately 450 species, spiny Solanum species constitute the largest monophyletic group in the Solanaceae family, but a high-quality genome assembly from this group is presently missing. We obtained a chromosome-anchored genome assembly of eggplant (Solanum melongena), containing 34,916 genes, confirming that the diploid gene number in the Solanaceae is around 35,000. Comparative genomic studies with tomato (S. lycopersicum), potato (S. tuberosum) and pepper (Capsicum annuum) highlighted the rapid evolution of miRNA:mRNA regulatory pairs and R-type defense genes in the Solanaceae, and provided a genomic basis for the lack of steroidal glycoalkaloid compounds in the Capsicum genus. Using parsimony methods, we reconstructed the putative chromosomal complements of the key founders of the main Solanaceae clades and the rearrangements that led to the karyotypes of extant species and their ancestors. From 10% to 15% of the genes present in the four genomes were syntenic paralogs (ohnologs) generated by the pre-γ, γ and T paleopolyploidy events, and were enriched in transcription factors. Our data suggest that the basic gene network controlling fruit ripening is conserved in different Solanaceae clades, and that climacteric fruit ripening involves a differential regulation of relatively few components of this network, including CNR and ethylene biosynthetic genes.

Cytogenetics and morphological delimitation between three species of Passiflora L. (subgenus Distephana Cervi).

Several studies on cytogenetic characterisation of passion flowers are helpful to elucidate doubts about taxa relationships, delimitation and classification into more coherent groups based on karyomorphological data. Molecular and conventional cytogenetic techniques were applied to three Passiflora species with red flowers, P.coccinea, P.vitifolia and P.tholozanii, for species karyotype relationships. Additionally, for descriptive morphology, were used flowers, leaves and seeds. Results describe for the first time the karyomorphological and chromosome number (2n=18) for P.tholozanii. anova was performed (P<0.05) and statistical significance for average chromosome size (CV: 16.53%) between species. Genomic insitu hybridisation (GISH) proved relationships between P.coccinea and P.tholozanii, which suggests a common origin, however, we could not identify hybridisation between genomic probes from P.vitifolia in P.tholozanii chromosomes. Among the species analysed, P.tholozanii has great similarity in karyotypic and morphology to P.coccinea but not to P.vitifolia. We suggest the inclusion of P.tholozanii in the same subgenus and section as P.coccinea based on the similarity in karyomorphological and morphological traits between the species. Additionally, GISH might indicate a common or hybrid origin of P.tholozanii.

A centromere satellite concomitant with extensive karyotypic diversity across the Peromyscus genus defies predictions of molecular drive

A common feature of eukaryotic centromeres is the presence of large tracts of tandemly arranged repeats, known as satellite DNA. However, these centromeric repeats appear to experience rapid evolution under forces such as molecular drive and centromere drive, seemingly without consequence to the integrity of the centromere. Moreover, blocks of heterochromatin within the karyotype, including the centromere, are hotspots for chromosome rearrangements that may drive speciation events by contributing to reproductive isolation. However, the relationship between the evolution of heterochromatic sequences and the karyotypic dynamics of these regions remains largely unknown. Here, we show that a single conserved satellite DNA sequence in the order Rodentia of the genus Peromyscus localizes to recurrent sites of chromosome rearrangements and heterochromatic amplifications. Peromyscine species display several unique features of chromosome evolution compared to other Rodentia, including stable maintenance of a strict chromosome number of 48 among all known species in the absence of any detectable interchromosomal rearrangements. Rather, the diverse karyotypes of Peromyscine species are due to intrachromosomal variation in blocks of repeated DNA content. Despite wide variation in the copy number and location of repeat blocks among different species, we find that a single satellite monomer maintains a conserved sequence and homogenized tandem repeat structure, defying predictions of molecular drive. The conservation of this satellite monomer results in common, abundant, and large blocks of chromatin that are homologous among chromosomes within one species and among diverged species. Thus, such a conserved repeat may have facilitated the retention of polymorphic chromosome variants within individuals and intrachromosomal rearrangements between species—both factors that have previously been hypothesized to contribute towards the extremely wide range of ecological adaptations that this genus exhibits.

Application of cytogenetic markers in the taxonomy of flat rock scorpions (Scorpiones: Hormuridae), with the description of Hadogenes weygoldti sp. n.

In the present study, we performed the first comparative cytogenetic study in Hadogenes species using both standard and molecular cytogenetic approaches. Information about the diploid set, number and distribution of 18S rDNA and telomeric sequences was obtained from three South African species, Hadogenes trichiurus (Gervais, 1843), H. zuluanus Lawrence, 1937 and H. weygoldti sp. n.. All species analysed differ considerably in the number of chromosomes (H. trichiurus 2n=48, H. zuluanus 2n=80, H. weygoldti sp. n. 2n=113). In contrast, the number of 18S rDNA clusters and distribution of telomeric sequences represent rather stable cytogenetic characters in Hadogenes. Within all karyotypes, we identified one pair of 18S rDNA clusters. The telomeric signals were exclusively on the terminal chromosomal regions. Interestingly, the chromosomal location of 18S rDNA clusters varied from terminal to interstitial in species karyotypes, indicating the presence of hidden structural chromosomal changes. Additionally, the present comparative study is complemented by the description of a new species, H. weygoldti sp. n., based on specific karyotype features and morphological characters. Finally, our cytogenetic results are compared with known chromosomal data of other Hadogenes species, and the use of cytogenetic approaches in the taxonomy of scorpions is discussed.

Karyotypes of Brazilian non-volant small mammals (Didelphidae and Rodentia): An online tool for accessing the chromosomal diversity.

We have created a database system named CIPEMAB (CItogenética dos PEquenos MAmíferos Brasileiros) to assemble images of the chromosomes of Brazilian small mammals (Rodents and Marsupials). It includes karyotype information, such as diploid number, karyotype features, idiograms, and sexual chromosomes characteristics. CIPEMAB facilitates quick sharing of information on chromosome research among cytogeneticists as well as researchers in other fields. The database contains more than 300 microscopic images, including karyotypic images obtained from 182 species of small mammals from the literature. Researchers can browse the contents of the database online (http://www.citogenetica.ufes.br). The system enables users to locate images of interest by taxa, and to display the document with detailed information on species names, authors, year of the species publication, and karyotypes pictures in different colorations. CIPEMAB has a wide range of applications, such as comparing various karyotypes of Brazilian species and identifying manuscripts of interest.

PROBLEMS SOLUTION OF SPECIAL IDENTIFICATION OF EISENIA CULTURAL POPULATIONS

PROBLEMS SOLUTION OF SPECIAL IDENTIFICATION OF EISENIA CULTURAL POPULATIONS

Heterochromatic and cytomolecular diversification in the Caesalpinia group (Leguminosae): Relationships between phylogenetic and cytogeographical data

The pantropical Caesalpinia group comprises 27 genera and approximately 205 species. The Neotropical species of the group are distributed in three main centers of diversity: the Andes, Mesoamerica (including Mexico, Central America, the southern USA and the Caribbean), and Northeastern Brazil. Our study investigates patterns of phylogenetic, environmental and geographical variation in an attempt to explain the karyotypic diversity which occurs within the Caesalpinia group. Cytogenetic analyses were based on chromosome number and morphology, CMA and DAPI heterochromatic bands, distribution of rDNA sites, and their molecular phylogenetic relationships based on the plastid markers matK, rps16, trnDT, trnL and ycf6 and the nuclear ribosomal marker ITS. Ecological differentiation among cytotypes was tested by comparing sets of climatic variables. In total, twenty species from ten genera of the Caesalpinia group were analysed, and all of them were found to have the same chromosome number (2n=24). CMA+/DAPI− bands were observed on the short arms of the acrocentric chromosomes in all of the species. Additionally, three different patterns were observed on the metacentric chromosomes: proximal CMA+/DAPI− bands, proximal CMA0/DAPI− bands and terminal CMA+/DAPI− bands. The 45S rDNA sites varied from eight to 14, always co-localizing with CMA+/DAPI− bands of acrocentrics, while 5S rDNA was localized in only a single chromosome pair in most species. A correlation between heterochromatic patterns and the geographic distributions/ecological niche of species was observed. Our analyses support some shared effects of the environment, when integrated with phylogeny and geography, on the CMA/DAPI variability. Thus, CMA+ heterochromatin is highly dynamic and its amplification/deamplification might be non-random, generating similar karyotypes in species which are not sister taxa in the molecular phylogeny but which co-occur in similar environments.

Cytogenetics of Two Onychostoma Species in Taiwan by Ag-NOR and 18S rDNA Profiles.

Chiao-Chuan Han, Tsair-Bor Yen, Nian-Cih Chen, and Mei-Chen Tseng (2017) Both Onychostoma barbatulum and O. alticorpus are primary freshwater fish in Taiwan. The former has been developed as an aquaculture species with high economic value, while the latter is a native endemic species in Taiwan. Understanding the cytogenetic information of these two species is necessary for their selected breeding, recovery, and management. In this study, Giemsa staining, silver-binding nucleolar organizer region (Ag-NOR), C-banding, and fluorescence in situ hybridization (FISH) with 18S ribosomal (r)DNA probes were used to analyze the cytogenetic characteristics. Results of Giemsa staining showed that the two Onychostoma species shared the same number of chromosomes, 2n = 50. Respective karyotype formulas of the female and male were 10 m + 22 sm + 10 st + 8 t and 11 m + 22 sm + 10 st + 7 t in O. barbatulum, and 14 m + 18 sm + 8 st + 10 t and 15 m + 18 sm + 8 st + 9 t in O. alticorpus. Karyotypes of both species showed a pair of heteromorphic chromosomes in male fish. Their sex determination should be the XX/XY system. Two pairs of Ag-NORs were found in O. barbatulum, but only one pair occurred in O. alticorpus. C-banding areas were observed on centromeres or telomeres of some chromosomes. FISH revealed different cytogenetic characters between these two species. The above cytogenetic information will contribute to species identification, population recovery, and advantages for breeding and management in the future.

Karyotype characterization and comparison of three hexaploid species of Bromus Linnaeus, 1753 (Poaceae).

Chromosome morphometry and nuclear DNA content are useful data for cytotaxonomy and to understand the evolutionary history of different taxa. For the genus Bromus Linnaeus, 1753, distinct ploidy levels have been reported, occurring from diploid to duodecaploid species. The geographic distribution of Bromus species has been correlated with chromosome number and ploidy level. In this study, the aims were to determine the nuclear genome size and characterize the karyotype of the South American Bromus species: Bromus auleticus Trinius ex Nees, 1829, Bromus brachyanthera Döll, 1878 and Bromus catharticus Vahl, 1791. The mean nuclear 2C value ranged from 2C = 12.64 pg for B. catharticus to 2C = 17.92 pg for B. auleticus, meaning a maximum variation of 2C = 5.28 pg, equivalent to 41.70%. Despite this significant difference in 2C value, the three species exhibit the same chromosome number, 2n = 6x = 42, which confirms their hexaploid origin. Corroborating the genome size, the chromosome morphometry (total, short- and long-arm length) and, consequently, the class differed among the karyotypes of the species. Based on the first karyograms for these Bromus species, some morphologically similar and several distinct chromosome pairs were found. Therefore, the karyotype characterization confirmed the hexaploid origin of the studied Bromus species, which differ in relation to the karyogram and the nuclear 2C value. Considering this, cytogenetics and flow cytometry can be used to discriminate Bromus species, contributing to taxonomy and systematic studies and providing information on the evolutionary history of this taxa.

Diversity, morphology and karyotypes of species from genus Neogobius (Perciformes; Gobiidae) at coastal zone of the Caspian Sea (Aktau city)

The paper presents the results on the diversity, morphology and karyotypes of species from the genus Neogobius collected during the summer seasons 2012-2016 in the shallow coastal zone of the Caspian Sea (Aktau city). A total of 6 species of goby fish belonging to two genera were found: Neogobius Iljin, 1927 and Ponticola Ilijn, 1927. Most species are widespread in the Northeast and Middle Caspian. The results of the morphological analysis did not reveal any significant differences between the populations of goby fish of the Northern and Middle Caspian, and also in comparison with the literature data. Chromosome kits and karyotypes detected in the observed gobies N. fluviatilis pallasi, N. melanostomus affinis, N. caspius, P. gorlap and P. syrman eurystomus are represented in the diploid set mainly by 46 acrocentric chromosomes, and in one species previously identified by us as N.sp (P.iljini) 2n = 40 chromosomes with a number of chromosome arms (NF) 46.

Description of the karyotypes of Stejneger's beaked whale (Mesoplodon stejnegeri) and Hubbs' beaked whale (M. carlhubbsi).

The genus Mesoplodon (Cetacea: Odontoceti: Ziphiidae) is one of the few cetacean genera with the karyotype 2n = 42. The 2n = 42 karyotype of M. europaeus and M. carlhubbsi is largely consistent with the general cetacean karyotype 2n = 44, although other 2n = 42 karyotypes do not exhibit clear homologies with the general cetacean karyotype. Therefore, the chromosomes of Mesoplodon species may be the key to understanding cetacean karyological evolution. In the present study, the male karyotypes of M. stejnegeri and M. carlhubbsi were examined. In both species, the diploid number of the male karyotype was 42. Both species had the following characteristics: 1) a huge subtelocentric X chromosome with a large C-block; 2) a small metacentric Y chromosome; 3) nucleolus organizer regions (NORs) in the terminal regions of a large autosome and one or two small metacentric autosomes; 4) small metacentric autosomes; 5) large submetacentric and subtelocentric autosomes; 6) less accumulated C-heterochromatin in the centromeric region; and 7) heteromorphism in C-heterochromatin accumulation between homologues. Characteristics 1 and 3 are peculiar to only the karyotypes of Mesoplodon species, whereas characteristics 4, 5, 6, and 7 are also found in the species with the general cetacean karyotype 2n = 44.