Comparative Cytogenetic Analysis Research Articles

Landscape of snake\u2019 sex chromosomes evolution spanning 85 MYR reveals ancestry of sequences despite distinct evolutionary trajectories

Most of snakes exhibit a ZZ/ZW sex chromosome system, with different stages of degeneration. However, undifferentiated sex chromosomes and unique Y sex-linked markers, suggest that an XY system has also evolved in ancestral lineages. Comparative cytogenetic mappings revealed that several genes share ancestry among X, Y and Z chromosomes, implying that XY and ZW may have undergone transitions during serpent’s evolution. In this study, we performed a comparative cytogenetic analysis to identify homologies of sex chromosomes across ancestral (Henophidia) and more recent (Caenophidia) snakes. Our analysis suggests that, despite ~ 85 myr of independent evolution, henophidians and caenophidians retained conserved synteny over much of their genomes. However, our findings allowed us to discover that ancestral and recent lineages of snakes do not share the same sex chromosome and followed distinct pathways for sex chromosomes evolution.

Karyotypic variability in Calliandra sect. Androcallis (Leguminosae–Caesalpinioideae)

Calliandra is a neotropical genus composed of 139 species with distribution in North, Central and South America. In this work, a comparative cytogenetic analysis of 10 species of the Androcallis section was performed by double staining with base-specific chromomycin A3 (CMA) and 4′,6-diamidino-2-phenylindole (DAPI). The DNA content of the species was also estimated by flow cytometry. This study revealed that the species C. macrocalyx, C. riparia, C. imperialis, C. ulei, C. spinosa and C. umbellifera are diploid with 2n = 2x = 16, C. fernandesii is tetraploid with 2n = 4x = 32, C. sessilis is octaploid with 2n = 8x = 64 and C. dysantha is decaploid with 2n = 10x = 80. This result revealed that polyploidy is one of the recurrent cytogenetic events in the evolution of the genus Calliandra. As for the number of CMA+ bands, it was possible to characterize each species. No AT-rich DAPI band was located on the chromosomes of the species. The results suggest that chromosomal rearrangements and polyploidy contributed to the evolution of Calliandra species, as demonstrated by the cytotaxonomic characterization in the genus.

Karyotype and putative chromosomal inversion suggested by integration of cytogenetic and molecular data of the fungus-farming ant Mycetomoellerius iheringi Emery, 1888.

Comparative cytogenetic analyses are being increasingly used to collect information on species evolution, for example, diversification of closely related lineages and identification of morphologically indistinguishable species or lineages. Here, we have described the karyotype of the fungus-farming ant Mycetomoellerius iheringi Emery, 1888 and investigated its evolutionary relationships on the basis of molecular and cytogenetic data. The M. iheringi karyotype consists of 2n = 20 chromosomes (2K = 18M + 2SM). We also demonstrated that this species has the classical insect TTAGG telomere organization. Phylogenetic reconstruction showed that M. iheringi is phylogenetically closer to M. cirratus Mayhé-Nunes & Brandão, 2005 and M. kempfi Fowler, 1982. We compared M. iheringi with other congeneric species such as M. holmgreni Wheeler, 1925 and inferred that M. iheringi probably underwent a major pericentric inversion in one of its largest chromosomes, making it submetacentric. We discussed our results in the light of the phylogenetic relationships and chromosomal evolution.

Cytomolecular diversity of the subtribe Laeliinae (Epidendroidae, Orchidaceae) suggests no relationship between genome size and heterochromatin abundance

The subtribe Laeliinae (Orchidaceae) comprises approximately 2000 species and 38 genera, with numerically stable karyotypes of 2n = 40 (x = 20) in most species. Cytomolecular and chromosome banding analyses have not yet been combined with phylogenetic studies, making the understanding of chromosomal evolution in the group more difficult. The present work sought to perform comparative cytogenetic analyses of representatives of the subtribe Laeliinae, followed by the interpretation of that data within an evolutive context. We analyzed 23 species from seven genera for their chromosome numbers and morphology, the distribution of CMA and DAPI bands, fluorescent in situ hybridization (FISH) with 5S and 35S rDNA and DNA quantification by flow cytometry. All of the species showed 2n = 40, suggesting an apparent macrostructural karyotypic stability, except the polyploids Encyclia alboxanthina, E. jenischiana, E. seidelii, Laelia gouldiana and Prosthechea faresiana (2n = 80). At least two CMA+/DAPI− terminal bands were observed in all analyzed species. Additionally, CMA+/DAPI− blocks were observed in the pericentromeric region of species of the genera Brassavola, Cattleya (except C. trianae) and Laelia. Terminal CMA−/DAPI+ bands were observed in representatives of Brassavola, Laelia and Guarianthe. The clade Brassavola + Cattleya + Laelia, that presented high number of heterochromatic bands, also showed expansions of the numbers of 5S rDNA sites. DNA contents varied from 2C = 2.85 pg (Prosthechea fragrans) to 2C = 5.76 pg (Laelia gouldiana) without relation with number of CMA/DAPI bands or 5S rDNA sites. The relationship between the amplification of repetitive DNAs (viewed here as rDNA sites or heterochromatic bands) and genome size variation is discussed and compared with other plant groups.

Comparative cytogenetic survey of the giant bonytongue Arapaima fish (Osteoglossiformes: Arapaimidae), across different Amazonian and Tocantins/Araguaia River basins

Abstract The South American giant fishes of the genus Arapaima, commonly known as pirarucu, are one of the most iconic among Osteoglossiformes. Previously cytogenetic studies have identified their karyotype characteristics; however, characterization of cytotaxonomic differentiation across their distribution range remains unknown. In this study, we compared chromosomal characteristics using conventional and molecular cytogenetic protocols in pirarucu populations from the Amazon and Tocantins-Araguaia river basins to verify if there is differentiation among representatives of this genus. Our data revealed that individuals from all populations present the same diploid chromosome number 2n=56 and karyotype composed of 14 pairs of meta- to submetacentric and 14 pairs of subtelo- to acrocentric chromosomes. The minor and major rDNA sites are in separate chromosomal pairs, in which major rDNA sites corresponds to large heterochromatic blocks. Comparative genomic hybridizations (CGH) showed that the genome of these populations shared a great portion of repetitive elements, due to a lack of substantial specific signals. Our comparative cytogenetic data analysis of pirarucu suggested that, although significant genetic differences occur among populations, their general karyotype patterns remain conserved.

Heterochromatin Bands and rDNA Sites Evolution in Polyploidization Events in Cynodon Rich. (Poaceae)

Cynodon is a genus with a wide distribution in tropical and subtropical areas. Ploidy levels in Cynodon range from diploid to hexaploid; hence, polyploidy is the most important driver of chromosome number variation in this genus. After polyploidization, structural rearrangements such as deletions, insertion, or duplications of DNA sequences frequently occur, allowing variation of chromosome morphology, size, and number. These events might result in a wide diversity of karyotypes, contributing to reproductive isolation, and consequently to speciation. In this study, we investigate the karyotype variation of Cynodon based on comparative cytogenetic analyses. We conducted chromosome counts, DNA quantification, CMA/DAPI double staining, and FISH mapping of 5S and 35S rDNA sites. Cytomolecular data were analyzed in a phylogenetic framework, in order to trace the evolutionary history of the karyotype variation considering polyploidy events in this group. Our results indicate that the most recent common ancestor of Cynodon had two 35S and 5S rDNA sites, two CMA bands, nine DAPI+ bands on the long arm, five DAPI+ bands on the short arm, and three DAPI+ bands in the pericentromeric region. During polyploidization events, there were losses and gains of heterochromatic sequences mainly on the short arms and centromeric regions.

Comparative analysis of the variability of the genetic structure of Anopheles messeae (Diptera, Culicidae) populations from Western Siberia and Eastern Kazakhstan

A comparison of the species composition of anopheles mosquitoes from the East Kazakhstan region and the south of Western Siberia has been carried out. A comparative cytogenetic analysis of An. messeae larvae from the southern and central parts of the range was done. The tendency of displacement of the “south-eastern” genocomplexes from the center of the An. messeae habitat to its southern borders has been observed.

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.

Adaptive Radiation from a Chromosomal Perspective: Evidence of Chromosome Set Stability in Cichlid Fishes (Cichlidae: Teleostei) from the Barombi Mbo Lake, Cameroon.

Cichlid fishes are the subject of scientific interest because of their rapid adaptive radiation, resulting in extensive ecological and taxonomic diversity. In this study, we examined 11 morphologically distinct cichlid species endemic to Barombi Mbo, the largest crater lake in western Cameroon, namely Konia eisentrauti, Konia dikume, Myaka myaka, Pungu maclareni, Sarotherodon steinbachi, Sarotherodon lohbergeri, Sarotherodon linnellii, Sarotherodon caroli, Stomatepia mariae, Stomatepia pindu, and Stomatepia mongo. These species supposedly evolved via sympatric ecological speciation from a common ancestor, which colonized the lake no earlier than one million years ago. Here we present the first comparative cytogenetic analysis of cichlid species from Barombi Mbo Lake using both conventional (Giemsa staining, C-banding, and CMA3/DAPI staining) and molecular (fluorescence in situ hybridization with telomeric, 5S, and 28S rDNA probes) methods. We observed stability on both macro and micro-chromosomal levels. The diploid chromosome number was 2n = 44, and the karyotype was invariably composed of three pairs of meta/submetacentric and 19 pairs of subtelo/acrocentric chromosomes in all analysed species, with the same numbers of rDNA clusters and distribution of heterochromatin. The results suggest the evolutionary stability of chromosomal set; therefore, the large-scale chromosomal rearrangements seem to be unlikely associated with the sympatric speciation in Barombi Mbo.

Comparative karyotype analysis among six species of Ipomoea based on two newly identified repetitive sequences.

Sweet potato is one of the most important crops worldwide; however, basic research in this crop is limited. In this study, we aimed to construct a detailed karyotype of six species of Ipomoea (hexaploid Ipomoea batatas and five related species, namely, one tetraploid, I. tabascana and four diploids, I. splendor-sylvae, I. trifida, I. tenuissima, and I. × leucantha) and understand the relationship among these species. Two satellite repeats (viz., Itf_1 and Itf_2) were identified from the diploid I. trifida genome sequence using RepeatExplorer on Galaxy. Together with the ribosomal DNA (rDNA), although without distinguishable chromosomes, a detailed karyotype was constructed for the six species. Our results showed a similar karyotype between I. tenuissima and I. × leucantha, indicating their close relationship. The signal distribution pattern of Itf_1, 45S rDNA combination, detected only in I. trifida, I. tabascana, and I. batatas, implied their close relationships. The chromosomes carrying 5S rDNA could be conserved among the six species as they always carried the Itf_2 signals, which generated a similar signal distribution pattern. The results enabled a detailed comparative cytogenetic analysis, providing valuable information to understand the relationship among these species and help assemble the genome sequence of the six species of Ipomoea.

Molecular Cytogenetics of Pisum sativum L. Grown under Spaceflight-Related Stress.

The ontogenesis and reproduction of plants cultivated aboard a spacecraft occur inside the unique closed ecological system wherein plants are subjected to serious abiotic stresses. For the first time, a comparative molecular cytogenetic analysis of Pisum sativum L. (Fabaceae) grown on board the RS ISS during the Expedition-14 and Expedition-16 and also plants of their succeeding (F1 and F2) generations cultivated on Earth was performed in order to reveal possible structural chromosome changes in the pea genome. The karyotypes of these plants were studied by multicolour fluorescence in situ hybridization (FISH) with five different repeated DNA sequences (45S rDNA, 5S rDNA, PisTR-B/1, microsatellite motifs (AG)12, and (GAA)9) as probes. A chromosome aberration was revealed in one F1 plant. Significant changes in distribution of the examined repeated DNAs in karyotypes of the “space grown” pea plants as well as in F1 and F2 plants cultivated on Earth were not observed if compared with control plants. Additional oligo-(GAA)9 sites were detected on chromosomes 6 and 7 in karyotypes of F1 and F2 plants. The detected changes might be related to intraspecific genomic polymorphism or plant cell adaptive responses to spaceflight-related stress factors. Our findings suggest that, despite gradual total trace contamination of the atmosphere on board the ISS associated with the extension of the space station operating life, exposure to the space environment did not induce serious chromosome reorganizations in genomes of the “space grown” pea plants and generations of these plants cultivated on Earth.

Comparative cytogenetics of four species of Thrichomys (Rodentia: Echimyidae).

Thrichomys Trouessart, 1880 is a genus of echimyid rodents endemic to South America, distributed from northeastern Brazil to Paraguay and Bolivia. Although all the recognized species of this genus have already been karyotyped, detailed comparative cytogenetic analyses have not been performed yet. We karyologically analyzed four species of Thrichomys from different Brazilian states. Our analyses included GTG- and CBG-banding, silver-staining of the nucleolar organizer regions (Ag-NORs), and fluorescent in situ hybridization (FISH) with telomeric and 45S rDNA probes. Comparative GTG-banding suggested that the interspecific variation may result from Robertsonian rearrangements, pericentric and paracentric inversions, centromere repositioning, and heterochromatin variation. FISH with a telomeric probe showed interspecies variation in interstitial telomeric sequences (ITs) distribution. Our results represent the most complete data on the cytogenetics of Thrichomys reported to date and give an insight into the chromosome evolution of this genus.

Comparative cytogenetic analysis of early reproductive losses depending of maternal age

Aim. Human reproduction characterized by a high incidence of aneuploidies. Approximately 99 % of conceptions with anomalies of karyotype terminate of pregnancy loss, mainly during the first 14 weeks of intrauterine development. The frequency and spectrum of karyotype anomalies in the chorionic villus of early reproductive losses were studied depending of maternal age. Methods. Banding cytogenetic and interphase mFISH with the centromeric probe panel for chromosomes 13, 14, 15, 16, 17, 18, 21, 22, X and Y were used. Results. The contribution of different karyotype abnormalities in the genesis of the early reproductive losses depends on the age of the woman, namely, with age significantly increases the proportion of aneuploidy due to autosomal trisomies and reduced contribution of polyploidy and gonosomal monosomy. The main autosomal trisomy in the material of lost pregnancies from women under the age of 35 is 16, 21 and 15, 22, 13 and 18 in order of decreasing frequency, and from older women 16, 15, 22, 21, 13 and 14. Conclusions. The structure and rate of karyotype anomalies in the material of lost pregnancies varies with maternal age.
 Keywords: early reproductive loss, maternal age, karyotype abnormalities.

Comparative cytogenetic analysis in Vigna sp. revealed by BAC-FISH

Vigna Savi species constitute a group of worldwide legumes of great socioeconomic importance. Progress in its genomic resources allowed the development of a consensus genetic map with a high-density of SNP markers and construction of Bacterial Artificial Chromosome (BAC) libraries. Fluorescent in situ hybridization (FISH) using BAC clones as probes (BAC-FISH) became a powerful tool for synteny and collinearity analyses among closely related species in several groups of plants. Previous work using BAC-FISH with probes of the P. vulgaris ‘BAT93’ library of V. unguiculata (Vu) and V. aconitifolia (Vac) chromosomes showed partial conservation of macrosynteny with chromosomal rearrangements. For a better understanding of the genomic organization and karyotype evolution in Vigna, we performed a comparative cytogenetic study with three Vigna species (2n = 22), using BAC-FISH. Four single-copy BACs of chromosome 3 and chromosome 11 of V. unguiculata (Vu3 and Vu11, respectively) were hybridized in situ on mitotic metaphase chromosomes of V. angularis (Van) and V. radiata (Vr). For chromosome 3, two Vu3 BACs (H31G07 and H50P11) were located in the same orientation at Vu, Van and Vr chromosomes, in interstitial regions in the short and long arms, respectively. These results suggest a conservation of synteny for both markers. On the other hand, H49E24 and H85I15 BACs were located respectively in terminal region in the short arm and subterminal region in the long arm of Vu11, while a distinct pattern was observed in Van, which showed both BACs at adjacent positions in the short arm. This suggests that a pericentric inversion involving BAC H85I15 occurred in one of these species. Based on the present results, associated with our previous works, the inversion observed on Vu11 seems to have occurred in V. unguiculata after Vigna and Phaseolus separation, since position of other BAC clones were different in Vu when compared to Vac, Van and Pv. These data demonstrate the feasibility of the BAC-FISH technique in comparative chromosome mapping, showing a break of macrosynteny among species of Phaseoloid clade. This is an initial step of an extensive macrosynteny study with BAC-FISH in Vigna.

The Karyotype of Amoeba borokensis from a “proteus-like” Amoeba Group (Amoebozoa: Euamoebida)

The karyotype of Amoeba borokensis was studied for the first time. At the metaphase of mitosis, this species has a haploid set of chromosomes (n = 27). This is exactly half of the diploid karyotype in Amoeba proteus (strain B). At first glance, it confirms the idea that has recently appeared that one species arises from another via multiple changes in chromosome number. However, comparative cytogenetic analysis revealed that four orthologous chromosomes from haploid sets of these two species were not distinguished by the pattern of DAPI-stained bands. It shows that the genetic distance between A. proteus and A. borokensis is higher than was believed earlier and these two species have diverged from each other. Analysis of data on the life cycles of A. proteus and A. borokensis shows that a kind of so-called “cyclic polyploidy” takes place in “proteus-like” amoebae. “Cyclic polyploidy” has recently been considered as an alternative to the sexual process for genetic recombination in agamic protists from different macrotaxons.

Comparative cytogenetic analysis of marine Palaemon species reveals a X1X1X2X2/X1X2Y sex chromosome system in Palaemon elegans

BackgroundThe maintenance of species and the promotion of speciation are closely related to chromosomal rearrangements throughout evolution. Decapoda represents the most species-rich order among crustaceans and, despite its ecological and economic importance, little is known about decapod karyology. We aim at cytogenetically characterizing two sympatric prawn species.ResultsAnalysis of mitotic metaphases and meiotic diakinesis of the common prawn Palaemon serratus and the rockpool prawn P. elegans, revealed considerable differences between their karyotypes including chromosome numbers and sex determination systems. The cytogenetic data for P. serratus showed a diploid number of 56 and the putative absence of heteromorphic sex chromosomes. However, the diploid chromosome number in P. elegans was 90 for females and 89 for males. The karyotype of the females consisted of the three largest acrocentric pairs and 42 submetacentric and metacentric pairs, while the karyotype of the males comprised a clearly identifiable large metacentric chromosome and two acrocentric pairs as well as the smaller 42 pairs. These results highlight the presence of the X1X1X2X2/X1X2Y multiple sex chromosome system in P. elegans, which constitute the only sexual system for Decapoda reported cytogenetically using modern techniques. The origin of this sex chromosome system is discussed. We hypothesize that the chromosome evolution within the genus could involve several fusion events giving rise to a reduction on the chromosome number in P. serratus. In both species, the major ribosomal genes were located in two chromosome pairs and hybridization signals of the telomeric sequences (TTAGGG)n were visualized at the telomeres of all chromosomes. C-banding revealed that, when present, constitutive heterochromatin had a predominantly telomeric distribution and no centromeric constitutive heterochromatin was observed.ConclusionsAlthough more comparative cytogenetic analyses are needed to clarify our hypotheses, the findings of this work indicate that the prawns of the genus Palaemon represent a promising model among Decapoda representatives to investigate the karyotype evolution and the patterns of sex chromosome differentiation.

Monophyletic Origin and Evolution of the Largest Crucifer Genomes.

Clade E, or the Hesperis clade, is one of the major Brassicaceae (Crucifereae) clades, comprising some 48 genera and 351 species classified into seven tribes and is distributed predominantly across arid and montane regions of Asia. Several taxa have socioeconomic significance, being important ornamental but also weedy and invasive species. From the comparative genomic perspective, the clade is noteworthy as it harbors species with the largest crucifer genomes but low numbers of chromosomes (n = 5-7). By applying comparative cytogenetic analysis and whole-chloroplast phylogenetics, we constructed, to our knowledge, the first partial and complete cytogenetic maps for selected representatives of clade E tribes and investigated their relationships in a family-wide context. The Hesperis clade is a well-supported monophyletic lineage comprising seven tribes: Anchonieae, Buniadeae, Chorisporeae, Dontostemoneae, Euclidieae, Hesperideae, and Shehbazieae. The clade diverged from other Brassicaceae crown-group clades during the Oligocene, followed by subsequent Miocene tribal diversifications in central/southwestern Asia. The inferred ancestral karyotype of clade E (CEK; n = 7) originated from an older n = 8 genome, which also was the purported progenitor of tribe Arabideae (KAA genome). In most taxa of clade E, the seven linkage groups of CEK either remained conserved (Chorisporeae) or were reshuffled by chromosomal translocations (Euclidieae). In 50% of Anchonieae and Hesperideae species, the CEK genome has undergone descending dysploidy toward n = 6 (-5). These genomic data elucidate early genome evolution in Brassicaceae and pave the way for future whole-genome sequencing and assembly efforts in this as yet genomically neglected group of crucifer plants.

Comparative cytomolecular analyses reveal karyotype variability related to biogeographic and species richness patterns in Bombacoideae (Malvaceae)

Bombacoideae is one out of nine subfamilies of Malvaceae and encompasses 160 tree species. The subfamily is karyotypically characterized by small and numerous chromosomes and is traditionally known by a remarkable inter- and intraspecific chromosome number variation. We conducted a comparative cytogenetic analysis to investigate karyotype diversity and chromosome evolution within Bombacoideae. To achieve this, we performed new chromosome counts, CMA/DAPI double staining, genome size estimations, and localization of 5S and 45S rDNA by fluorescence in situ hybridization for 21 species distributed across the Bombacoideae phylogeny. We performed ancestral states reconstruction analyses to elucidate chromosome evolution and provide insights into the systematics and evolution of Bombacoideae in comparison with other Malvaceae species. Newly generated data on chromosome number on Bombacoideae revealed diploids (Ochroma (2n = 84), Cavanillesia, Pochota, Pseudobombax (2n = 88), and Pachira (2n = 92)) and polyploids (Adansonia digitata (2n = 160) and Eriotheca species (2n = ca. 194 and 2n = 276)). For most species, in situ hybridization revealed karyotype, with two pairs of 45S rDNA sites co-located with CMA+ bands, and 5S rDNA sites in only one chromosome pair. Taken together, our results provide support to the hypothesis of karyotypic stability in Bombacoideae. Only the Pachira s.l. clade displayed some variability in ploidy level, number of CMA+ bands and 45S rDNA sites, and genome size compared to other Bombacoideae clades. The Striated bark clade was characterized by comparatively small genomes and low cytomolecular variability. Karyotypic data were related to biogeographic and species richness patterns of Bombacoideae.

Karyotypic evolution of the Medicago complex: sativa-caerulea-falcata inferred from comparative cytogenetic analysis

BackgroundPolyploidy plays an important role in the adaptation and speciation of plants. The alteration of karyotype is a significant event during polyploidy formation. The Medicago sativa complex includes both diploid (2n = 2× = 16) and tetraploid (2n = 2× = 32) subspecies. The tetraploid M. ssp. sativa was regarded as having a simple autopolyploid origin from diploid ssp. caerulea, whereas the autopolyploid origin of tetraploid ssp. falcata from diploid form ssp. falcata is still in doubt. In this study, detailed comparative cytogenetic analysis between diploid to tetraploid species, as well as genomic affinity across different species in the M. sativa complex, were conducted based on comparative mapping of 11 repeated DNA sequences and two rDNA sequences by a fluorescence in situ hybridization (FISH) technique.ResultsFISH patterns of the repeats in diploid subspecies caerulea were highly similar to those in tetraploid subspecies sativa. Distinctly different FISH patterns were first observed in diploid ssp. falcata, with only centromeric hybridizations using centromeric and multiple region repeats and a few subtelomeric hybridizations using subtelomeric repeats. Tetraploid subspecies falcata was unexpectedly found to possess a highly variable karyotype, which agreed with neither diploid ssp. falcata nor ssp. sativa. Reconstruction of chromosome-doubling process of diploid ssp. caerulea showed that chromosome changes have occurred during polyploidization process.ConclusionsThe comparative cytogenetic results provide reliable evidence that diploid subspecies caerulea is the direct progenitor of tetraploid subspecies sativa. And autotetraploid ssp. sativa has been suggested to undergo a partial diploidization by the progressive accumulation of chromosome structural rearrangements during evolution. However, the tetraploid subspecies falcata is far from a simple autopolyploid from diploid subspecies falcata although no obvious morphological change was observed between these two subspecies.

Highest Diploid Number Among Gymnotiformes: First Cytogenetic Insights into Rhabdolichops (Sternopygidae).

We report the first comparative cytogenetic analysis of two species from electrogenic fish of genus Rhabdolichops (Sternopygidae, Gymnotiformes): Rhabdolichops troscheli and Rhabdolichops cf eastwardi. R. troscheli has 2n = 54 (fundamental number [FN] = 66), whereas R. cf. eastwardi has 2n = 74 (FN = 78). C-banding revealed centromeric constitutive heterochromatin in both species. Ag-NORs mapped on pair 6 in R. troscheli and pair 30 in R. cf eastwardi. Fluorescense in situ hybridization with 18S rDNA probes confirmed the Ag-NOR staining results and revealed additional (presumably silent) ribosomal genes on pairs 12, 13, 21, 23, 26, and 27 in R. cf eastwardi. 5S rDNA was found on the centromeres of pair 7 in both species. Telomeric probes showed only distal locations. Dispersed signal patterns were obtained using probes for retrotransposons Rex1 and Rex3. Histone H1 and H3 genes were found together on pair 6 in R. cf eastwardi. The high diploid number found in Rhabdolichops suggests that chromosome fission may have contributed to its chromosomal evolution, phylogenetic relationship of the Sternopygidae suggests that this increase in diploid number could be a synapomorphic characteristic of genus Rhabdolichops. Although both species are phylogenetically close related, their karyotype structure has undergone divergent evolutionary directions. All in all, our results strongly suggest that R. cf eastwardi experencied recent intense genome reorganization.