Karyotypes of the most primitive catfishes (Teleostei: Siluriformas: Diplomystidae)

Karyotypes of Diplomystes composensis and Diplomystes nahuelbutaensis were the same diploid number (n= 56).The chromosome formula for D. composensis was 16 metacentric + 24 submetacentric + 8 subtelocentric + 8 telocentric chromosomes and for D. nahuelbutaensis was 14 metacentric + 26 submetacentric + 8 subtelocentric +8 telocentric chromosomes. In contrast, the differences in the chromosomal C-banding patterns between these species was large. For instance, chromosome pairs 5,6, and 7 of D. nahuelbutaensis showed heterochromatic centromeres and pairs 23, 24, 27, and 28 were entirely heterochromotic. Diplomystes composensis showed conspicuous C-banded blocks in pairs 7, 24, and 25 (chromosome pair 7 had one heterochromatic arm, chromosome pair 24 was entirely heterochromatic, and chromosome pair 25 had heterochromatin close to centromere). Comparison with other ostariophysan karyotypes (e.g. gymnotiforms, characiforms, and cypriniforms), does not allow any conclusions about the ploesiomorphic catfish condition, because the karyotypes of the outgroups are too variable. A synapomorphy shared by characiforms, gymnotiforms, and diplomystid catfishes is the presence of more metacentric to submetacentric than substelocentric to telocentric chromosomes. Cypriniforms are more primitive because they have more subtelocentric to telocentric than metacentric to submetacentric chromosomes.     

Karyotype and Chromosomal Location of 18S–28S and 5S Ribosomal DNA in the Scallops Pecten maximus and Mimachlamys varia (Bivalvia: Pectinidae)

This work describes the karyotype and chromosomal location of the ribosomal DNA (rDNA) of Pecten maximus and Mimachlamys varia, two commercial scallop species from Europe. According to the chromosome centromeric index values found, the karyotype of P. maximus is composed of 1 metacentric, 2 metacentric–submetacentric, 1 telocentric–subtelocentric and 15 telocentric pairs, and that of M. varia of 4 metacentric, 2 subtelocentric–submetacentric, 9 subtelocentric, 3 subtelocentric–telocentric and 1 telocentric–subtelocentric pairs. In P. maximus, 18S-28S rDNA was located by FISH on a metacentric–submetacentric pair, and in M. varia on a subtelocentric–submetacentric pair using both silver staining and FISH. PCR amplification of the 5S rDNA unit yielded a single product of about 460 bp (P. maximus) and 450 bp (M. varia), that used as probe revealed a 5S rDNA site on a telocentric pair in P. maximus and a subtelocentric pair in M. varia. Two-color FISH or sequential silver staining of 5S rDNA-FISH-metaphases corroborated that the two gene families are located on different chromosomes in both species. A comparative analysis of the data allowed the inference of karyotypic relationships within scallops.     

Cytogenetic characterisation of the Caspian Pond Turtle,Mauremys caspica in Golestan and Mazandaran provinces,Iran (Reptilia: Testudines)

Cytogenetic characteristics of the Caspian Pond Turtle, Mauremys caspica, in Golestan and Mazandaran provinces in the northern part of Iran show that the chromosome number is 2n?=?52 and the arm number NF?=?78. The karyotype consisted of 9 metacentric (M), 1 submetacentric (SM), 3 subtelocentric (ST) and 13 telocentric (T) chromosome pairs. The Centromeric Index ranges from 11.79 to 45.68, the arm ratio between 1.18 and 7.47, the relative length between 1.60 and 11.46, and the length variation between 1.05 and 7.48. Average total length of the chromosomes is 65.27 µm. The largest chromosome in this species is a pair of the metacentric chromosome. Location of NOR was determined on chromosome pair no. 10.     

Cytogenetic characterisation of the razor shells Ensis directus (Conrad, 1843) and E. minor (Chenu, 1843) (Mollusca: Bivalvia)

The European razor shell Ensis minor (Chenu 1843) and the American E. directus (Conrad 1843) have a diploid chromosome number of 38 and remarkable differences in their karyotypes: E. minor has four metacentric, one metacentric–submetacentric, five submetacentric, one subtelocentric and eight telocentric chromosome pairs, whereas E. directus has three metacentric, two metacentric–submetacentric, six submetacentric, six subtelocentric and two telocentric pairs. Fluorescent in situ hybridisation (FISH) using a major ribosomal DNA probe located the major ribosomal genes on one submetacentric chromosome pair in both species; FISH with a 5S ribosomal DNA (5S rDNA) probe rendered one chromosomal (weak) signal for E. minor and no signal for E. directus, supporting a more dispersed organisation of 5S rDNA compared to the major ribosomal genes. The vertebrate telomeric sequence (TTAGGG) _n was located on both ends of each chromosome, and no interstitial signals were detected. In this work, a comparative karyological analysis was also performed between the four Ensis species analysed revealing that the three European species studied so far, namely E. minor, E. siliqua (Linné 1758) and E. magnus Schumacher 1817 show more similarities among them than compared to the American species E. directus. In addition, clear karyotype differences were found between the morphologically similar species E. minor and E. siliqua.     

Speciation via hybrid dysgenesis: negative evidence from the Drosophila affinis subgroup

Differences in karyotypic structure are compared with reported isozyme differences in three Mediterranean species of Patella. In addition, the karyotypic structure of Patella is discussed in terms of the karyotypic variability of Archaeogastropoda. Both P. lusitanica and P. caerulea have a haploid complement of n=9 (6 metacentric, 1 submetacentric, 1 subtelocentric, 1 telocentric chromosome in P. lusitanica and 6 metacentric, 1 submetacentric, 2 telocentric chromosome in P. caerulea). P. aspera, although regarded as morphologically more closely related to P. caerulea, has a haploid complement of only n=8 (7 metacentric and 1 submetacentric chromosomes).     

Karyotypes of two Antarctic fishes,Notothenia gibberifrons andNotothenia coriiceps neglecta

The chromosomes of two species of Antarctic fishes,Notothenia (Gobionotothen) gibberifrons andNotothenia (Notothenia) coriiceps neglecta, were prepared by the air-drying method at the Polish Antarctic Station “Henryk Arctowski” during the austral summer 1984–1985. ForN. (G.) gibberifrons the diploid number is2n = 46 consisting of 2 metacentric (m) pairs, 1 submetacentric (sm) pair and 20 telocentric (t) or subtelocentric (st) pairs. ForN. (N.) coriiceps neglecta the diploid number is 2n = 22 consisting of 9 m pairs, 1 sm pair and 1st pair. Some aspects of karyological evolution of these fishes are discussed.     

Cytogenetics of the razor clam Solen marginatus (Mollusca: Bivalvia: Solenidae)

The razor clam Solen marginatus has a diploid chromosome number of 38. The karyotype consists of one metacentric/submetacentric, three submetacentric/metacentric, five submetacentric, one submetacentric/subtelocentric, one subtelocentric/submetacentric, six subtelocentric and two telocentric chromosome pairs. Staining with chromomycin A3 revealed bright positive bands subcentromerically in the long arms of one medium-sized subtelocentric pair, while DAPI staining showed uniform fluorescence in all chromosomes of the complement. Fluorescence in situ hybridization using an 18S-5.8S-28S rDNA probe locates these loci at the subcentromeric region of one subtelocentric pair and at the subtelomeric region of another subtelocentric pair.     

不同地理区域鲫鱼染色体银染核仁组织者的比较研究

本文对不同地理区域的鲫鱼(Carassius auratus)—滇池高背鲫、低背鲫、方正银鲫(C.auratusgibelio)的核型及核仁组织者NORs进行了比较研究,并对高背鲫来源作些初步探讨,结果如下: 1.低背鲫Carassius auratus (back low type):2n=100,22m+30sm+48t.st,NORs=4,出现于第5—6对亚中着丝粒染色体短臂。 2.滇池高背鲫Carassius auratus(back high type):2n=156,30m+46sm+80t.st,NORs=6,出现于第5—7对亚中着丝粒染色体短臂。 3.方正银鲫C.auratus gibelio:2n=162,32m+52sm+78t.st NORs=4,出现于第5—6对亚中着粒染色体短臂。     

Chromosomal differentiation of Hyla nana and Hyla sanborni (Anura,Hylidae) with a description of NOR polymorphism in H. nana

Specimens of Hyla nana and Hyla sanborni from a syntopic population were studied cytogenetically. These species are morphologically very similar and are frequently misidentified, confused with each other. Both species had a diploid chromosome number, 2n = 30. However, the karyotypes of H. nana and H. sanborni differed considerably from each other in the number of submetacentric and telocentric chromosomes. The two species also differed in their primary NOR-bearing chromosomes (metacentric pair 13 in H. nana and telocentric pair 12 in H. sanborni). Additional nucleolus organizer regions (NORs) were detected by Ag-NOR staining and FISH in chromosome pairs 1, 5, 6, 12, and 14 in seven specimens of H. nana. Thus, a total of six patterns of NOR were identified. These differences in karyotype and in NOR location allowed the unambiguous identification of syntopic individuals of the two species. However, the chromosomal morphology of both species differed from that reported for populations from other geographic regions, suggesting that a systematic reevaluation of this group of Hyla may be necessary.     

Chromosomal polymorphism in Rattus rattus (L.) collected in Kusudomari and Misima

Summary Chromosomes of Rattus rattus (L.), collected in Kusudomari (Nagasaki) and Misima (Sizuoka) were examined. The karyotype revealed a remarkable heteromorphism in chromosome no. 1. The homozygotic, i.e. standard type, was characterized by 13 pairs of telocentric and 7 pairs of metacentric chromosomes. Chromosome pair no. 1 was telocentric. X and Y chromosomes were also telocentrics. 18.4 per cent of rats from Kusudomari and 40 per cent from Misima showed heteromorphic pair in chromosome no. 1. One chromosome of the heteromorphic pair is conspicuous by the subtelocentric centromere. Total length of the telocentric chromosome of no. 1 is almost the same as of its subtelocentric partner. These facts indicate that the subtelocentric no. 1 chromosome might have arisen by a centromeric inversion of the telocentric chromosome. Individuals homozygous for the subtelocentric no. 1 chromosome could not be found in either population. The difference in the frequency of the dimorphics collected in Kusudomari and Misima was statistically significant. Possible causes of the difference are discussed.Dedicated to Professor H. Bauer on the occasion of his sixtieth birthday. — Contributions from the National Institute of Genetics, Misima, Japan, No. 533     

Chromosomal analysis of twelve species of Microhylidae (Anura) from Madagascar

The karyotypes of four species of Dyscophinae and eight species of Cophylinae were analyzed. The chromosome number was 2n=26 in all cases. Between the two subfamilies a difference in the form of the karyotype was observed; the chromosomes show a gradual decrease in length in the Dyscophinae, whereas in the Cophylinae the karyotype demonstrates a clear discontinuity of size between pairs 5 and 6.Chromosomal polymorphism was found in Plethodontohyla tuberata, the chromosomes of pair 4 were subtelocentric in the homozygous specimens, whereas this pair showed a subtelocentric and a submetacentric chromosome of equal length in the heterozygous one, suggesting a pericentric inversion. Although in the Cophylinae the chromosome number is constant, the number of chromosome arms is variable. Pericentric inversions seem to play an important role in the chromosomal evolution of the Cophylinae.     

Note on the karyotype and NOR phenotype of leuciscine fish Acanthobrama marmid (Osteichthyes, Cyprinidae)

The karyotype and major ribosomal sites as revealed using silver staining of Anatolian leuciscine cyprinid fish Acanthobrama marmid were studied. The diploid chromosome number was invariably 2n = 50. Karyotype consisted of eight pairs of metacentric, 13 pairs of submetacentric and four pairs of subtelocentric to acrocentric chromosomes. The largest chromosome pair of the complement was subtelo-to acrocentric characteristically, which is a characteristic cytotaxonomic marker for representatives of the cyprinid lineage Leuciscinae. The nucleolar organizer regions (NORs) were detected in the telomeres of two pairs of medium sized submeta-to subtelocentric chromosomes. No heteromorphic sex chromosomes were found. The karyotype pattern of A. marmid is nearly identical to that found in most other representatives of the Eurasian leuciscine cyprinids, while the multiple NOR phenotype appears to be more derived as opposed to a uniform one, ubiquitous in this group.     

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.     

Chromosomes of Syrphidae

This report describes the karyotypes of fourteen species of the tribe Chrysotoxini (Diptera, Syrphidae) with the single genus Chrysotoxum. The species are listed in the Table on p. 240. All have 2n=10 chromosomes, usually consisting of short apparently telocentric sex chromosomes plus two subtelocentric and two submetacentric pairs of autosomes.     

Cytogenetic characterisation of the ornamental freshwater fish, Piabucus melanostomus (Iguanodectinae) from Brazilian wetlands and its relation with species of Characidae basal group

The genus Piabucus is the only member of the subfamily Iguanodectinae found in the Pantanal of Mato Grosso State, where it is represented by Piabucus melanostomus. P. melanostomus from the Paraguay and Bento Gomes Rivers of the Pantanal wetlands were analysed using conventional and molecular cytogenetic techniques to cytogenetically characterise the species and broaden the knowledge of the subfamily. The results indicated no sex-related heteromorphisms. The diploid number for the species was 2n = 50 chromosomes, which were divided into six metacentric, eight submetacentric, 24 subtelocentric, and 12 acrocentric with a fundamental number (FN) of 88. Heterochromatin was visualised using the C-banding technique, which showed that it was mainly distributed in the centromeric and pericentromeric region of most chromosomes, but larger blocks were observed on the long arms of large subtelocentric chromosomes (8, 9, 10, 13, and 20 pairs). Nucleolar organising regions (Ag-NOR) were observed in the p-subterminal region of one subtelocentric chromosome pair (9) with a remarkable size polymorphism between homologues in individuals from the Paraguay River, which was confirmed using the FISH technique with 18S rDNA. In this population, in all individuals studied, one of the homologous shows block considerably larger. The karyotype was compared with those of other subfamilies considered basal in Characidae, according to morphological data.     

ZZ/ZW sex chromosome system in an undescribed species of the genus Apareiodon (Characiformes, Parodontidae)

The chromosomes of an undescribed species of the genus Apareiodon (Characiformes, Parodontidae) from the Verde River, a headwater affluent of the Tibagi River (Paraná State, Brazil), were investigated using conventional Giemsa and Ag stainings, C-banding, CMA(3) fluorescence and fluorescent in situ hybridization (FISH) using 18S and 5S rDNA probes. The diploid chromosome number was 2n = 54, with the karyotype composed of 48 meta/submetacentric and six subtelocentric chromosomes in males, and 47 meta/submetacentric + seven subtelocentric chromosomes in females. The difference is hypothesized to be due to a ZZ/ZW heteromorphic sex chromosome system, a cytotaxonomic characteristic previously observed only in some species of the genus Parodon (family Parodontidae). The presence of similar and/or identical heteromorphic sex chromosome systems might suggest that species of the genera Parodon and Apareiodon bearing ZZ/ZW heteromorphic sex chromosomes likely constitute a monophyletic group, a hypothesis to be tested by a robust phylogeny of the family.     

Karyotypes and cellular DNA contents of three species of the subfamily Clupeinae

Karyotypes of three species of the subfamily Clupeinae collected from northern Japan were analyzed by in vitro methods and their cellular DNA contents were measured using an integrating microdensitometer.Sardinella zunasi andSardinops melanostictus show very similar karyotypes: 2n = 48, consisting of acrocentric or subtelocentric chromosomes with a gradual decrease in chromosome size, but with differences in cellular DNA of 2.32 and 2.69pg/cell respectively.Clupea pallasii differs from the aforementioned species in karyotype: 2n = 52, consisting of 6 metacentric or submetacentric chromosomes and 46 acrocentric or subtelocentric chromosomes, with a cellular DNA content of 1.96 pg/cell. The results showed two different modes in karyological evolution within the subfamily Clupeinae, i.e. an increase of cellular DNA content without apparent change in karyotype, as shown bySardinella zunasi andSardinops melanostictus, and less change in cellular DNA content but with marked change in karyotype, as shown byClupea pallasii.     

Chromosomal mapping of the major and minor ribosomal genes, (GATA)n and (TTAGGG)n by one-color and double-color FISH in the toadfish Halobatrachus didactylus (Teleostei: Batrachoididae)

The karyotype of Halobatrachus didactylus presents 46 chromosomes, composed of eight metacentric, 18 submetacentric, four subtelocentric, and 16 acrocentric chromosomes. The results of FISH showed that the major ribosomal genes were located in the terminal position of the short arm of a large submetacentric chromosome. They also showed a high variation in the hybridization signals. The products of amplification of 5S rDNA produced bands of about 420 pb. The PCR labeled products showed hybridization signals in the subcentromeric position of the long arm of a submetacentric chromosome of medium size. Double-color FISH indicated that the two ribosomal families are not co-located since they hybridizated in different chromosomal pairs. Telomeres of all the chromosomes hybridized with the (TTAGGG) _n probe. The GATA probe displayed a strong signal in the long arm of a submetacentric chromosome of medium size, in the subcentromeric position. The double-color FISH showed that the microsatellite GATA and the 5S rDNA gene are located in different chromosomal pairs. The majority presence of GATA probes in one pair of chromosomes is unusual and considering its distribution through different taxa it could be due to evolutionary mechanisms of heterochromatine accumulation, leading to the formation of differentiated sex chromosomes.     

Occurrence of two cytotypes in <Emphasis Type="Italic">Bryconamericus</Emphasis> aff. <Emphasis Type="Italic">iheringii</Emphasis> (Characidae): karyotype analysis by C- and G-banding and replication bands

Cytogenetic analyses of Bryconamericus aff. iheringii specimens from the upper Paraná River basin (State of Paraná, Brazil) are provided. They had 2n = 52 chromosomes and two cytotypes with variations in their karyotypic formulae: cytotype I with 12 metacentric, 18 submetacentric, 8 subtelocentric and 14 acrocentric chromosomes with a fundamental number (FN) of 90; cytotype II with 8 metacentric, 28 submetacentric, 6 subtelocentric and 10 acrocentric chromosomes with a fundamental number (FN) of 94. Differences in C- and G-band patterns between the cytotypes, distinguishing marker chromosomes for each karyotype, were reported. The R-band pattern by 5-bromodeoxyuridine incorporation was obtained in chromosomes of the cytotype II sample. In some metaphases, the second pair of submetacentric chromosomes is distinctive: its short arm is heterochromatic (positive C-band), corresponding to a late replication region. In the same cytotype, a G- and R-band size heteromorphism w as recorded in the long arm of pair 9 (submetacentric). These methodologies revealed an actual karyotypic differentiation in the B. aff. iheringii population analyzed. Morphometrical comparative analyses and a discussion of evolutionary aspects of chromosome diversification in species of this genus are provided as well.     

颈棱蛇核型和Ag－NORs的研究

本文研究了云南产颈棱蛇的核型和Ａｇ－ＮＯＲｓ。其Ｚｎ＝４６,由８对大染色体和１５对小染色体组成,大染色体中Ｎｏ．６、８为亚中着丝粒染色体,其余均为端或亚端着丝粒染色体。在Ｎｏ．２的末端有一明显的次缢痕,常常只在一条同源染色体上可见。第４对大型染色体为性染色体,雌性为ＺＷ型,其中Ｚ染色体较大,而Ｗ染色体长度仅为Ｚ染色体的三分之二。一对核仁组织者（ＮＯＲｓ）位于Ｎｏ．２末端,其位置与次缢痕位置相对应。文中还对颈棱蛇的分类和进化进行了讨论。