rDNA Sites Research Articles

Occurrence of structural polymorphism and supernumerary chromosomes in a population of Parodon nasus (Parodontidae)

AbstractThe family Parodontidae is a small group of fish that has distinct morphological differences. Despite its conserved diploid number, structural cytogenetic polymorphisms involving sex chromosomes are commonly described in this group. Conversely, reports on numerical polymorphisms owing to the occurrence of supernumerary chromosomes are rare. To better understand the karyotype evolution of this group, we analyzed specimens of Parodon nasus collected in the Tres Bocas/PR stream, applying different cytogenetic techniques. All individuals presented 54 meta-submetacentric chromosomes, except for three females, which exhibited structural polymorphism. The NOR occurred on a pair of submetacentric chromosomes. Heterochromatin was distributed in some pericentromeric areas, predominating in the terminal regions. We detected B microchromosomes in four of the collected individuals, which were heterochromatic and bearers of 18S rDNA sites. This work deals with the first description of these chromosomes in the f...

Chromosome mapping in Abracris flavolineata (De Geer, 1773) (Orthoptera) from the Iguaçu National Park - Foz do Iguaçu, Paraná, Brazil.

In this paper, we present the cytomolecular analysis of a population of Abracris flavolineata collected in the largest fragment of the Brazilian Atlantic forest, the Iguaçu National Park. The diploid number in males was 23 (22+X0), with two large pairs (1–2), 7 medium (3–9), 2 small (10–11) and the X chromosome of medium size. Heterochromatic blocks were evident in the pericentromeric regions of all chromosomes. Heterogeneity in the distribution of heterochromatin was observed, with a predominance of DAPI+ blocks. However, some chromosomes showed CMA3+ blocks and other DAPI+/CMA3+ blocks. The 18S rDNA sites were distributed on the short arms of 5 pairs. In two of these pairs, such sites were in the same chromosome bearing 5S rDNA, and one of the bivalents, they were co-located. Histone H3 genes were found on one bivalent. The results added to the existing cytogenetic studies provided evidence of great karyotypic plasticity in the species. This pliancy may be the result of vicariant events related to the geographical distribution of different populations of A. flavolineata.

Chromosomal Mapping of Repetitive DNA Sequences in the Genus Bryconamericus (Characidae) and DNA Barcoding to Differentiate Populations.

The mapping of repetitive DNA sites by fluorescence in situ hybridization has been widely used for karyotype studies in different species of fish, especially when dealing with related species or even genera presenting high chromosome variability. This study analyzed three populations of Bryconamericus, with diploid number preserved, but with different karyotype formulae. Bryconamericus ecai, from the Forquetinha river/RS, presented three new cytotypes, increasing the number of karyotype forms to seven in this population. Other two populations of Bryconamericus sp. from the Vermelho stream/PR and Cambuta river/PR exhibited interpopulation variation. The chromosome mapping of rDNA sites revealed unique markings among the three populations, showing inter- and intrapopulation variability located in the terminal region. The molecular analysis using DNA barcoding complementing the cytogenetic analysis also showed differentiation among the three populations. The U2 small nuclear DNA repetitive sequence exhibited conserved features, being located in the interstitial region of a single chromosome pair. This is the first report on its occurrence in the genus Bryconamericus. Data obtained revealed a karyotype variability already assigned to the genus, along with polymorphism of ribosomal sites, demonstrating that this group of fish can be undergoing a divergent evolutionary process, constituting a substantive model for studies of chromosomal evolution.

Karyotype Diversity in Doradidae (Siluriformes, Doradoidea) and Presence of the Heteromorphic ZZ/ZW Sex Chromosome System in the Family.

Karyotypes and other chromosomal markers as revealed by conventional and molecular cytogenetic protocols in four species of the catfish family Doradidae from the Araguaia-Tocantins river basin, namely Hassar wilderi, Leptodoras cataniae, Tenellus leporhinus and Tenellus trimaculatus were examined. All species had diploid chromosome number 2n = 58 and karyotypes dominated by biarmed chromosomes, simple NOR phenotype, that is, one chromosome pair bearing this site in terminal position, but some differences in karyotypes and distribution of constitutive heterochromatin, position of rDNA sites. Such characteristics appeared species-specific. A ZZ/ZW sex chromosome system was found in Tenellus trimaculatus, resulting likely from the amplification of the heterochromatin, followed by a paracentric inversion. Our results confirmed low karyotype differentiation observed until now among representatives of this endemic catfish family.

Chromosomal Evolution and Cytotaxonomy in Wrasses (Perciformes; Labridae).

The wrasses (family Labridae) represent a suitable model to understand chromosomal evolution and to test the efficacy of cytotaxonomy since they display a remarkable karyotypic variation, rarely reported in marine Perciformes, as well as a high number of species and complex systematics. Therefore, we provided new chromosomal data in 5 labrids from South Atlantic (Doratonotus megalepis, Halichoeres dimidiatus, Halichoeres penrosei, Thalassoma noronhanum, and Xyrichtys novacula) and carried out a detailed comparative analysis of karyotypic data in Labridae using multivariate approaches. Basal diploid values (2n = 48) were observed in most of species studied in the present work but D. megalepis (2n = 46), along with distinct karyotype formulae. Single 18S rDNA sites interspersed with GC-rich heterochromatin were also commonly reported except for both Halichoeres species (2 18S rDNA-bearing pairs), following a species-specific pattern. These data show the high rates of chromosomal evolution in wrasses, ranging from microstructural rearrangements to centric fusions. A revision of chromosomal data in Labridae based on multivariate analysis of 74 taxa allowed inferring karyoevolutionary trends within tribes and genera of wrasses. The dendrogram obtained was in agreement with recent systematic hypotheses. In spite of the independent occurrence of some chromosomal rearrangements, karyoevolutionary trends could be identified within tribes of Labridae. Moreover, the karyotypic features are also suitable as cytotaxonomic markers of wrasses.

Cytogenetic and Molecular Data Support the Occurrence of Three Gymnotus Species (Gymnotiformes: Gymnotidae) Used as Live Bait in Corumbá, Brazil: Implications for Conservation and Management of Professional Fishing.

In the Pantanal of Mato Grosso do Sul, electric fish (Gymnotus spp.) are the primary source of live bait, accounting for more than three-quarters of total sales. Based on chromosomal and molecular markers, the present study attempted to identify the Gymnotus species used as bait in the region of Corumbá, Mato Grosso do Sul, Brazil. Three species were detected, based on their distinct karyotypes: G. paraguensis (2n = 54), G. sylvius (2n = 40), and G. pantanal (2n = 39-40, X1X2Y/X1X1X2X2), with no evidence being found of interspecific hybrids. All three species presented a single nucleolar organizer regions (NOR) (heterochromatin CMA3+/DAPI-) and pericentromeric heterochromatin in almost all chromosomes, with a few distal and/or interstitial blocks. G. sylvius and G. pantanal had one and two pairs of chromosomes with 5S rDNA sites, respectively, while G. paraguensis had 17 chromosome pairs with these markers. The three species formed well-defined clusters in the DNA barcoding analysis. The integrated analysis of the cytogenetic and DNA barcoding data confirmed that the diversity of Gymnotus species exploited as live bait in the study region has been underestimated. These findings indicate that the markers analyzed represent valuable tools for the conservation and fishery management of the Gymnotus stocks exploited.

Evolutional dynamics of 45S and 5S ribosomal DNA in ancient allohexaploid Atropa belladonna

BackgroundPolyploid hybrids represent a rich natural resource to study molecular evolution of plant genes and genomes. Here, we applied a combination of karyological and molecular methods to investigate chromosomal structure, molecular organization and evolution of ribosomal DNA (rDNA) in nightshade, Atropa belladonna (fam. Solanaceae), one of the oldest known allohexaploids among flowering plants. Because of their abundance and specific molecular organization (evolutionarily conserved coding regions linked to variable intergenic spacers, IGS), 45S and 5S rDNA are widely used in plant taxonomic and evolutionary studies.ResultsMolecular cloning and nucleotide sequencing of A. belladonna 45S rDNA repeats revealed a general structure characteristic of other Solanaceae species, and a very high sequence similarity of two length variants, with the only difference in number of short IGS subrepeats. These results combined with the detection of three pairs of 45S rDNA loci on separate chromosomes, presumably inherited from both tetraploid and diploid ancestor species, example intensive sequence homogenization that led to substitution/elimination of rDNA repeats of one parent. Chromosome silver-staining revealed that only four out of six 45S rDNA sites are frequently transcriptionally active, demonstrating nucleolar dominance. For 5S rDNA, three size variants of repeats were detected, with the major class represented by repeats containing all functional IGS elements required for transcription, the intermediate size repeats containing partially deleted IGS sequences, and the short 5S repeats containing severe defects both in the IGS and coding sequences. While shorter variants demonstrate increased rate of based substitution, probably in their transition into pseudogenes, the functional 5S rDNA variants are nearly identical at the sequence level, pointing to their origin from a single parental species. Localization of the 5S rDNA genes on two chromosome pairs further supports uniparental inheritance from the tetraploid progenitor.ConclusionsThe obtained molecular, cytogenetic and phylogenetic data demonstrate complex evolutionary dynamics of rDNA loci in allohexaploid species of Atropa belladonna. The high level of sequence unification revealed in 45S and 5S rDNA loci of this ancient hybrid species have been seemingly achieved by different molecular mechanisms.

Genomic characterisation of Arachis porphyrocalyx (Valls & C.E. Simpson, 2005) (Leguminosae): multiple origin of Arachis species with x = 9.

The genus Arachis Linnaeus, 1753 comprises four species with x = 9, three belong to the section Arachis: Arachis praecox (Krapov. W.C. Greg. & Valls, 1994), Arachis palustris (Krapov. W.C. Greg. & Valls, 1994) and Arachis decora (Krapov. W.C. Greg. & Valls, 1994) and only one belongs to the section Erectoides: Arachis porphyrocalyx (Valls & C.E. Simpson, 2005). Recently, the x = 9 species of section Arachis have been assigned to G genome, the latest described so far. The genomic relationship of Arachis porphyrocalyx with these species is controversial. In the present work, we carried out a karyotypic characterisation of Arachis porphyrocalyx to evaluate its genomic structure and analyse the origin of all x = 9 Arachis species. Arachis porphyrocalyx showed a karyotype formula of 14m+4st, one pair of A chromosomes, satellited chromosomes type 8, one pair of 45S rDNA sites in the SAT chromosomes, one pair of 5S rDNA sites and pericentromeric C-DAPI+ bands in all chromosomes. Karyotype structure indicates that Arachis porphyrocalyx does not share the same genome type with the other three x = 9 species and neither with the remaining Erectoides species. Taking into account the geographic distribution, morphological and cytogenetic features, the origin of species with x = 9 of the genus Arachis cannot be unique; instead, they originated at least twice in the evolutionary history of the genus.

Interregional cytogenetic comparisons in Halichoeres and Thalassoma wrasses (Labridae) of coastal and insular regions of the southwestern Atlantic.

The distribution patterns of marine biodiversity are complex, resulting from vicariant events and species dispersion, as well as local ecological and adaptive conditions. Furthermore, the wide geographic distribution of some species may be hindered by biogeographical barriers that can interfere in the gene flow. Cytogenetic analyses in marine fishes, especially those involving populations in small remote insular environments, remain scarce. In the Western Atlantic, species of wrasses from the genera Halichoeres and Thalassoma occur in biogeographic arrangements that make it possible to analyze cytogenetic patterns between coastal and widely separated island populations. Species of these genera were punctually analyzed in some Atlantic regions. In this study, we compared several chromosomal features, such as karyotype macrostructure, heterochromatic patterns, patterns of base-specific fluorochromes, Ag-NORs, and 18S and 5S ribosomal sites in Thalassoma noronhanum, Halichoeres poeyi, and Halichoeres radiatus individuals from distinct coastal or insular regions of Atlantic. Notably, all of them are characterized by multiple 18S and 5S rDNA sites with syntenic arrangements in some chromosome pairs. Individuals of T. noronhanum (between the insular regions of Rocas Atoll and Fernando de Noronha Archipelago - FNA) and H. poeyi (coastal areas from Northeastern Brazil) show no detectable differences among their cytogenetic patterns. On the other hand, H. radiatus from FNA and São Pedro and São Paulo Archipelago exhibit differences in the frequency of rDNA sites that could suggest some level of population structuring between these insular regions. Interregional cytogenetic inventories of marine species with wide geographic distribution need to be rapidly expanded. These data will allow a better understanding of the level of chromosomal stability between vast oceanic spaces, which may be less than previously thought.

Dynamics of 45S rDNA sites in the cell cycle: fragile sites and chromosomal stability in Lolium and Festuca.

Analyses carried out with fluorescence in situ hybridization (FISH) in C-metaphases of the Lolium-Festuca complex have shown the occurrence of spontaneous fragile sites (FSs) in 45S rDNA regions. FSs are expressed as gaps but they do not result in breaks or chromosomal fragments in these species. These gaps have high DNA condensation observed as thin chromatin fibers that connect the apparent segments of the fragile chromosome, allowing for genomic stability. Assessing the behavior of these regions in the cell cycle of Lolium and Festuca species may lead to a better understanding of the dynamics that preserve stability during cell division. Furthermore, it is interesting to track the dynamics of chromosomes bearing 45S rDNA sites in the cell cycle as well as to observe the expression of FSs with no effect of the mitotic block. We observed variation in both the number and size of 45S FISH signals from the S/G2 phases of interphase and from prophase to anaphase where gaps in 45S rDNA sites also were observed. The change in the degree of condensation of the 45S site begins in the S/G2 phase and appears to be related to the transcriptional demand. Taking into account that the number of 45S rDNA sites tends to be re-established when cells reach telophase, we suggest that the chromatin fiber goes back to the normal condensation level to the anaphase (after segregation), allowing for the approximation of chromosome segments and ensuring dynamics that favor the genomic stability of these species.

Genome differentiation, natural hybridisation and taxonomic relationships among Eleocharis viridans, E. niederleinii and E. ramboana (Cyperaceae)

The role of natural hybridisation and genome changes in the differentiation and speciation of Eleocharis (Cyperaceae) was addressed through the study of the following three closely related species of the polyphyletic series Tenuissimae: Eleocharis viridans Kük. ex Osten, E. ramboana R.Trevis & Boldrini and E. niederleinii Boech., which often reproduce asexually. Molecular and cytogenetic data were used to understand the genomic and karyotypic relationships in the group. Genomes were compared using internal transcribed spacer–cleaved amplified polymorphic sequence (ITS-CAPS) marker and confirmed with random amplified polymorphic DNA, which allowed identification of different genetic groups, with clear evidence of natural hybrids. Karyotype analysis showed numerical variation from 2n = 20–42, with occurrence of chromosome heteromorphisms and polymorphisms, including variability in 35S rDNA site numbers. Meiotic studies demonstrated irregular pairing in some samples, which is associated with hybridisation and asexual reproduction. Genomic in situ hybridisation (GISH) reactions were conducted using two well defined genetic groups as probes, with 2n = 20 and normal meiosis. Probes were tested against each one of the genetic groups and showed positive, partial and negative GISH results, which supported the molecular analysis data. The results indicated that the three studied species are undergoing an intense process of genomic and karyotypic re-arrangement, which results in overlapping of morphological and genomic characteristics. The present study has exemplified the value of an integrative taxonomic approach to solve conflicts in species delimitation in groups undergoing hybridisation.

Mechanisms of Chromosomal Diversification in Species of Rineloricaria (Actinopterygii: Siluriformes: Loricariidae).

Cytogenetic studies in fish of the Rineloricaria genus have already shown a high variation in diploid number (2n). Along with fusion/fission events for 2n alteration, inversions contribute to the diversification of chromosome formulae within this group. The present study assessed different populations/species of the Rineloricaria aiming to describe the karyotype organization of its members and understand the mechanisms that lead to the variation of chromosome numbers. Cytogenetic data showed distinct karyotype organization among Rineloricaria populations/species studied, ranging in diploid number from 46 to 64 chromosomes, syntopic species and two karyomorphs in Rineloricaria pentamaculata. Using ribosomal DNAs (rDNAs) and TTAGGGn probes by fluorescence in situ hybridization in species with low diploid numbers, we detected sites of 18S rDNA, 5S rDNA, and TTAGGGn in centromeric regions of metacentric chromosomes, which participated in chromosome rearrangements like centric fusions. In species with high 2n, centric fissions probably occurred in karyotypic diversification. In this study, we assessed the telomeric instability, chromosomal breaks, and rearrangements due to interstitial telomeric site vestiges detection, in addition to the probable role of rDNAs in chromosome fusions in karyotypic diversification of this group.

Unraveling the karyotype structure of the spurges Euphorbia hirta Linnaeus, 1753 and E. hyssopifolia Linnaeus, 1753 (Euphorbiaceae) using genome size estimation and heterochromatin differentiation.

Euphorbia Linnaeus, 1753 (Euphorbiaceae) is one of the most diverse and complex genera among the angiosperms, showing a huge diversity in morphologic traits and ecologic patterns. In order to improve the knowledge of the karyotype organization of Euphorbia hirta (2n = 18) and Euphorbia hyssopifolia (2n = 12), cytogenetic studies were performed by means of conventional staining with Giemsa, genome size estimations with flow cytometry, heterochromatin differentiation with chromomycin A3 (CMA) and 4’,6-diamidino-2-phenylindole (DAPI) and Giemsa C-banding, fluorescent in situ hybridization (FISH) with 45S and 5S rDNA probes, and impregnation with silver nitrate (AgNO3). Our results revealed small metacentric chromosomes, CMA+/DAPI0 heterochromatin in the pericentromeric regions of all chromosomes and CMA+/DAPI− in the distal part of chromosome arms carriers of nucleolar organizing regions (NORs). The DNA content measurements revealed small genomes for both species: Euphorbia hirta with 2C = 0.77 pg and Euphorbia hyssopifolia with 2C = 1.41 pg. After FISH procedures, Euphorbia hirta, and Euphorbia hyssopifolia presented three and four pairs of terminal 45S rDNA sites, respectively, colocalizing with CMA+ heterochromatic blocks, besides only one interstitial pair of 5S rDNA signals. Additionally, the maximum number of active NORs agreed with the total number of observed 45S rDNA sites. This work represents the first analysis using FISH in the subfamily Euphorbioideae, revealing a significant number of chromosomal markers, which may be very helpful to understand evolutionary patterns among Euphorbia species.

RDNA Loci Evolution in the Genus Glechoma (Lamiaceae).

Glechoma L. (Lamiaceae) is distributed in eastern Asia and Europe. Understanding chromosome evolution in Glechoma has been strongly hampered by its small chromosomes, constant karyotype and polyploidy. Here phylogenetic patterns and chromosomal variation in Glechoma species are considered, using genome sizes, chromosome mapping of 5S and 35S rDNAs by fluorescence in situ hybridisation (FISH), and phylogenetic analyses of internal transcribed spacers (nrITS) of 35S rDNA and 5S rDNA NTS sequences. Species and populations of Glechoma are tetraploid (2n = 36) with base chromosome number of x = 9. Four chromosomes carry pericentric 5S rDNA sites in their short arms in all the species. Two to four of these chromosomes also carry 35S rDNA in subterminal regions of the same arms. Two to four other chromosomes have 35S rDNA sites, all located subterminally within short arms; one individual possessed additional weak pericentric 35S rDNA signals on three other chromosomes. Five types of rDNA locus distribution have been defined on the basis of 35S rDNA variation, but none is species-specific, and most species have more than one type. Glechoma hederacea has four types. Genome size in Glechoma ranges from 0.80 to 0.94 pg (1C), with low levels of intrapopulational variation in all species. Phylogenetic analyses of ITS and NTS sequences distinguish three main clades coinciding with geographical distribution: European (G. hederacea–G. hirsuta), Chinese and Korean (G. longituba), and Japanese (G. grandis). The paper presents the first comparative cytogenetic analyses of Glechoma species including karyotype structure, rDNA location and number, and genome size interpreted in a phylogenetic context. The observed variation suggests that the genus is still in genomic flux. Genome size, but not rDNA loci number and distribution, provides a character for species delimitation which allows better inferences of interspecific relationships to be made, in the absence of well-defined morphological differentiation.

Detecting Mechanisms of Karyotype Evolution in Heterotaxis (Orchidaceae).

The karyotype is shaped by different chromosome rearrangements during species evolution. However, determining which rearrangements are responsible for karyotype changes is a challenging task and the combination of a robust phylogeny with refined karyotype characterization, GS measurements and bioinformatic modelling is necessary. Here, this approach was applied in Heterotaxis to determine what chromosome rearrangements were responsible for the dysploidy variation. We used two datasets (nrDNA and cpDNA, both under MP and BI) to infer the phylogenetic relationships among Heterotaxis species and the closely related genera Nitidobulbon and Ornithidium. Such phylogenies were used as framework to infer how karyotype evolution occurred using statistical methods. The nrDNA recovered Ornithidium, Nitidobulbon and Heterotaxis as monophyletic under both MP and BI; while cpDNA could not completely separate the three genera under both methods. Based on the GS, we recovered two groups within Heterotaxis: (1) "small GS", corresponding to the Sessilis grade, composed of plants with smaller genomes and smaller morphological structure, and (2) "large GS", corresponding to the Discolor clade, composed of plants with large genomes and robust morphological structures. The robust karyotype modeling, using both nrDNA phylogenies, allowed us to infer that the ancestral Heterotaxis karyotype presented 2n = 40, probably with a proximal 45S rDNA on a metacentric chromosome pair. The chromosome number variation was caused by ascending dysploidy (chromosome fission involving the proximal 45S rDNA site resulting in two acrocentric chromosome pairs holding a terminal 45S rDNA), with subsequent descending dysploidy (fusion) in two species, H. maleolens and H. sessilis. However, besides dysploidy, our analysis detected another important chromosome rearrangement in the Orchidaceae: chromosome inversion, that promoted 5S rDNA site duplication and relocation.

Co-located 18S/5S rDNA arrays: an ancient and unusual chromosomal trait in Julidini species (Labridae, Perciformes).

Wrasses (Labridae) are extremely diversified marine fishes, whose species exhibit complex interactions with the reef environment. They are widely distributed in the Indian, Pacific and Atlantic oceans. Their species have displayed a number of karyotypic divergent processes, including chromosomal regions with complex structural organization. Current cytogenetic information for this family is phylogenetically and geographically limited and mainly based on conventional cytogenetic techniques. Here, the distribution patterns of heterochromatin, GC-specific chromosome regions and Ag-NORs, and the organization of 18S and 5S rDNA sites of the Atlantic species Thalassoma noronhanum (Boulenger, 1890), Halichoeres poeyi (Steindachner, 1867), Halichoeres radiatus (Linnaeus, 1758), Halichoeres brasiliensis (Bloch, 1791) and Halichoeres penrosei Starks, 1913, belonging to the tribe Julidini were analyzed. All the species exhibited 2n=48 chromosomes with variation in the number of chromosome arms among genera. Thalassoma noronhanum has 2m+46a, while species of the genus Halichoeres Rüppell, 1835 share karyotypes with 48 acrocentric chromosomes. The Halichoeres species exhibit differences in the heterochromatin distribution patterns and in the number and distribution of 18S and 5S rDNA sites. The occurrence of 18S/5S rDNA syntenic arrangements in all the species indicates a functionally stable and adaptive genomic organization. The phylogenetic sharing of this rDNA organization highlights a marked and unusual chromosomal singularity inside the family Labridae.

Chromosome painting of telomeric repeats reveals new evidence for genome evolution in peanut

Interspecific hybridization is an important approach to improve cultivated peanut varieties. Cytological markers such as tandem repeats will facilitate alien gene introgression in peanut. Telomeric repeats have also been frequently used in chromosome research. Most plant telomeric repeats are (TTTAGGG)n that are mainly distributed at the chromosome ends, although interstitial telomeric repeats (ITRs) are also commonly identified. In this study, the telomeric repeat was chromosomally localized in 10 Arachis species through sequential GISH (genomic in situ hybridization) and FISH (fluorescence in situ hybridization) combined with 4’,6-diamidino-2-phenylindole (DAPI) staining. Six ITRs were identified such as in the centromeric region of chromosome Bi5 in Arachis ipaënsis, pericentromeric regions of chromosomes As5 in A. stenosperma, Bho7 in A. hoehnei and Av5 in A. villosa, nucleolar organizer regions of chromosomes As3 in A. stenosperma and Adi3 in A. diogoi, subtelomeric regions of chromosomes Bho9 in A. hoehnei and Adu7 in A. duranensis, and telomeric region of chromosome Es7 in A. stenophylla. The distributions of the telomeric repeat, 5S rDNA, 45S rDNA and DAPI staining pattern provided not only ways of distinguishing different chromosomes, but also karyotypes with a higher resolution that could be used in evolutionary genome research. The distribution of telomeric repeats, 5S rDNA and 45S rDNA sites in this study, along with inversions detected on the long arms of chromosomes Kb10 and Bho10, indicated frequent chromosomal rearrangements during evolution of Arachis species.

Further evidence for the variability of the 18S rDNA loci in the family Tingidae (Hemiptera, Heteroptera).

As of now, within the lace bug family Tingidae (Cimicomorpha), only 1.5% of the species described have been cytogenetically studied. In this paper, male karyotypes of Stephanitis caucasica, Stephanitis pyri, Physatocheila confinis, Lasiacantha capucina, Dictyla rotundata and Dictyla echii were studied using FISH mapping with an 18S rDNA marker. The results show variability: the major rDNA sites are predominantly located on a pair of autosomes but occasionally on the X and Y chromosomes. All currently available data on the distribution of the major rDNA in the Tingidae karyotypes are summarized and shortly discussed. Our main concern is to clarify whether the chromosomal position of rDNA loci can contribute to resolving the phylogenetic relationships among the Tingidae taxa.

Karyotype and Mapping of Repetitive DNAs in the African Butterfly Fish Pantodon buchholzi, the Sole Species of the Family Pantodontidae

The monophyletic order Osteoglossiformes represents one of the most ancestral groups of teleosts and has at least 1 representative in all continents of the southern hemisphere, with the exception of Antarctica. However, despite its phylogenetic and biogeographical importance, cytogenetic data in Osteoglossiformes are scarce. Here, karyotype and chromosomal characteristics of the lower Niger River population of the African butterfly fish Pantodon buchholzi, the sole species of the family Pantodontidae (Osteoglossiformes), were examined using conventional and molecular cytogenetic approaches. All specimens examined had 2n = 46 chromosomes, with a karyotype composed of 5 pairs of metacentric, 5 pairs of submetacentric, and 13 pairs of acrocentric chromosomes in both sexes. No morphologically differentiated sex chromosomes were identified. C-bands were located in the centromeric/pericentromeric region of all chromosomes and were associated with the single AgNOR site. FISH with ribosomal DNA probes revealed that both 5S and 18S rDNA were present in only 1 pair of chromosomes each, but did not colocalize. CMA₃⁺ bands were observed near the telomeres in several chromosome pairs and also at the 18S rDNA sites. The mapping of di- and trinucleotide repeat motifs, Rex6 transposable element, and U2 snRNA showed a scattered distribution over most of the chromosomes, but for some microsatellites and the U2 snRNA also a preferential accumulation at telomeric regions. This study presents the first detailed cytogenetic analysis in the African butterfly fish by both conventional and molecular cytogenetic protocols. This is the first of a series of further cytogenetic and cytogenomic studies on osteoglossiforms, aiming to comprehensively examine the chromosomal evolution in this phylogenetically important fish order.

Chromosome markers confirm origin of Heliconia hybrids and triploids

Heliconia L., the only genus in the Heliconiaceae family, comprises about 380 species with high ornamental potential. However, the identification of genotypes—mainly based on morphological characteristics—has generated synonyms. Therefore, it becomes necessary to apply novel techniques to differentiate genotypes and elucidate the origin of hybrids and triploids. The aim of the present work was the cytogenetic characterization of 18 Heliconia genotypes, including three hybrids, two triploids and their possible parent plants, by means of chromosome counting, staining with the fluorochromes CMA and DAPI, and FISH for 45S and 5S rDNA sites. The analyses revealed 16 diploid (2n = 2x = 24) and two triploid genotypes (2n = 3x = 36), with new counts for eight genotypes, including the triploid ‘Suriname Sassy’. The karyotypes were symmetric, with chromosomes varying from 0.88 to 3.35 µm. Regarding the CMA/DAPI staining and FISH, one CMA+/DAPI0/5S rDNA band was observed in the proximal region of two and three small chromosomes in the diploid and triploid genotypes, respectively. The CMA++/DAPI−/45S rDNA markings varied from two to four sites per genotype, revealing some interesting heteromorphisms. The distribution of 5S and 45S rDNA sites, both CMA-positive, corroborated the origin of the triploid genotypes ‘Sassy’ and ‘Suriname Sassy’ from diploid genotypes of H. psittacorum, as well as the origin of the hybrids of H. psittacorum × H. spathocircinata (‘Golden Torch’ and ‘Golden Torch Adrian’) and H. caribaea × H. bihai cv. ‘Jacquinii’ from their respective parent species.