Stable Chromosome Number Research Articles

Cytological analysis of the diploid-like inheritance of newly synthesized allotetraploid wheat.

Polyploidization is a process which is related to species hybridization and whole genome duplication. It is widespread among angiosperm evolution and is essential for speciation and diversification. Allopolyploidization is mainly derived from interspecific hybridization and is believed to pose chromosome imbalances and genome instability caused by meiotic irregularity. However, the self-compatible allopolyploid in wild nature is cytogenetically and genetically stable. Whether this stabilization form was achieved in initial generation or a consequence of long term of evolution was largely unknown. Here, we synthesized a series of nascent allotetraploid wheat derived from three diploid genomes of A, S*, and D. The chromosome numbers of the majority of the progeny derived from these newly formed allotetraploid wheat plants were found to be relatively consistent, with each genome containing 14 chromosomes. In meiosis, bivalent was the majority of the chromosome configuration in metaphase I which supports the stable chromosome number inheritance in the nascent allotetraploid. These findings suggest that diploidization occurred in the newly formed synthetic allotetraploid wheat. However, we still detected aneuploids in a proportion of newly formed allotetraploid wheat, and meiosis of these materials present more irregular chromosome behavior than the euploid. We found that centromere pairing and centromere clustering in meiosis was affected in the aneuploids, which suggest that aneuploidy may trigger the irregular interactions of centromere in early meiosis which may take participate in promoting meiosis stabilization in newly formed allotetraploid wheat.

A cytosystematic study of the Dianthus virgineus complex (Caryophyllaceae) in the Central Mediterranean

AbstractEuropean wild carnations (Dianthus) are represented by a high number of taxa organized in unresolved taxonomies. In particular, taxa belonging to the Dianthus virgineus L. complex in the Central Mediterranean have been delimited mainly with qualitative morphological data and still await quantitative investigations, which are vital to understand boundaries and relations among plant diversity groups. Here, we examine the phenotypic features of nuclear genome organization testing for species boundaries in this complex. We have studied the chromosome number, the total haploid length (THL), and the relative genome size (RGS) in 122 populations belonging to 25 out of 33 taxa of the complex. All the studied populations have 2n = 2x = 30 chromosomes, and the THL ranges from 14.09 to 20.71 μm. Genome size estimations support the absence of polyploidization events, but show a certain degree of variation (0.318–0.423 arbitrary units). The RGS variation is not in agreement with current taxonomic treatment, but rather shows a geographical pattern, with higher values in Sicily and Sardinia. No correlation between the THL and the RGS was detected, possibly due to the stable chromosome number and the small size of chromosomes. A number of evolutionary unique groups lower than the number of currently accepted taxa may be hypothesized.

Chromosome number of <i>Carex brevispicula</i> (Cyperaceae), a sedge endemic to Korea

<i>Carex brevispicula</i> (Cyperaceae) is endemic to Korea and is characterized by constricted achenes, short lateral spikes, and awned staminate and pistillate scales. The species classified in sect. <i>Mitratae</i> occurs throughout South Korea, perennating on mountains and/or rocky slopes under half shadow conditions. Meiotic chromosomes of the species were examined in this study, in which 33 meiotic cells from seven populations were found to be less than 2 μm long with non-constricted chromosomes (<i>n</i> = 34<sub>II</sub>). The stable chromosome number may be related to the narrow geographical distribution and/or distinct achene morphology. Further investigations of the distribution, morphological character variation, and chromosome characteristics should be conducted with closely related taxa to understand the derivation of the species and its endemism in Korea.

Cytogenetic characterization and karyotype evolution in six Macroptilium species (Leguminosae).

Macroptilium (Benth.) Urb. is a neotropical legume genus from the subtribe Phaseolinae. The investigated species present a stable chromosome number (2n=22), but differ in their karyotype formulae, suggesting the presence of chromosome rearrangements. In this work, we comparatively analysed the karyotypes of six species (Macroptilium atropurpureum, Macroptilium bracteatum, Macroptilium erythroloma, Macroptilium gracile, Macroptilium lathyroides, and Macroptilium martii) from the two main clades that form the genus. Heterochromatin distribution was investigated with chromomycin A3 (CMA)/4',6-diamidino-2-phenylindole (DAPI) staining and fluorescent in situ hybridization was used to localize the 5S and 35S ribosomal DNA (rDNA) sites. Single copy bacterial artificial chromosomes (BACs) previously mapped in the related genera Phaseolus L. and Vigna Savi were used to establish chromosome orthologies and to investigate possible rearrangements among species. CMA+/DAPI- bands were observed, mostly associated with rDNA sites. Additional weak, pericentromeric bands were observed on several chromosomes. Although karyotypes were similar, species could be differentiated mainly by the number and position of the 5S and 35S rDNA sites. BAC markers demonstrated conserved synteny of the main rDNA sites on orthologous chromosomes 6 and 10, as previously observed for Phaseolus and Vigna. The karyotypes of the six species could be differentiated, shedding light on its karyotype evolution.

Chromosomes of Asian Cyprinid Fishes: Genomic Differences in Conserved Karyotypes of 'Poropuntiinae' (Teleostei, Cyprinidae).

The representatives of cyprinid lineage 'Poropuntiinae' with 16 recognized genera and around 100 species form a significant part of Southeast Asian ichthyofauna. Cytogenetics are valuable when studying fish evolution, especially the dynamics of repetitive DNAs, such as ribosomal DNAs (5S and 18S) and microsatellites, that can vary between species. Here, karyotypes of seven 'poropuntiin' species, namely Cosmochilus harmandi, Cyclocheilichthys apogon, Hypsibarbus malcomi, H. wetmorei, Mystacoleucus chilopterus, M. ectypus, and Puntioplties proctozysron occurring in Thailand were examined using conventional and molecular cytogenetic protocols. Variable numbers of uni- and bi-armed chromosomes indicated widespread chromosome rearrangements with a stable diploid chromosome number (2n) of 50. Examination with fluorescence in situ hybridization using major and minor ribosomal probes showed that Cosmochilus harmandi, Cyclocheilichthys apogon, and Puntioplites proctozystron all had one chromosomal pair with 5S rDNA sites. However, more than two sites were found in Hypsibarbus malcolmi, H. wetmorei, Mystacoleucus chilopterus, and M. ectypus. The number of chromosomes with 18S rDNA sites varied amongst their karyotypes from one to three; additionally, comparative genomic hybridization and microsatellite patterns varied among species. Our results reinforce the trend of chromosomal evolution in cyprinifom fishes, with major chromosomal rearrangements, while conserving their 2n.

EfGD: the Erianthus fulvus genome database.

Erianthus fulvus (TaxID: 154759) is a valuable germplasm resource in sugarcane breeding and research and has excellent agronomic traits, such as drought resistance, cold resistance, barren tolerance and high brix. With a stable chromosome number (2n = 20) and a small genome (0.9 Gb), it is an ideal candidate for research on sugarcane. Next-generation sequencing technology has enabled a growing number of studies to focus on genomics. Due to the large amount of omics data available, a centralized platform is necessary for ensuring the consistency, independence and maintainability of these large-scale datasets through storage, analysis and integration. Here, we present a comprehensive database for the E. fulvus genome, EfGD. By using the new high-quality reference genome and its annotations, the EfGD provides the largest whole-genome sequencing reference dataset for E. fulvus, which archives 27 165 protein-coding genes and 55 564 488 SNPs from 202 newly resequenced genomes. Furthermore, we created a user-friendly graphical interface for visualizing genomic diversity, population structure and evolution and provided other tools on an open platform. Database URL: https://efgenome.ynau.edu.cn

The landscape of karyotype diversity in Marantaceae

Marantaceae is a pantropically distributed family, which includes species with ornamental and food potential. Chromosome number change and its outcomes, such as nuclear 2C value variation, provide valuable information for cytotaxonomy as well as about evolution and speciation of the different taxa. Here, we aimed to determine the 2n chromosome number of nine species and measure the nuclear 2C value of 23 species representing eight genera of Marantaceae. The chromosome number of six species and the 2C nuclear value of 18 species were reported for the first time. In addition, we performed the morphometric characterization and 5S rDNA mapping in Monotagma plurispicatum, which exhibited the lowest 2n chromosome number (2n = 12). The species exhibited notable chromosome number differences, 2n = 12, 24, 26, 36, 44, 46, 48 or 50 chromosomes. For each species, we found a stable somatic chromosome number. The mean 2C nuclear value also varied between the species from 2C = 0.63 pg (Ischnosiphon leucophaeus) to 13.49 pg (Saranthe eichleri), representing an intergeneric variation reaching 2,041%. M. plurispicatum chromosome number, karyogram and 5S rDNA mapping (chromosome 3) evidenced that its diploidy with complement set x = 6, with two metacentric (1 and 5), three submetacentric (3, 4 and 6), and one acrocentric (2) chromosome. Considering our findings and previously published data, we reinforce that polyploidy play an important role in the interspecific variation of chromosome number and/or nuclear genome size in Marantaceae, and that these genomic changes influence diversification and speciation in this family.

Isolation and characterization mesenchymal stem cells from red panda (Ailurus fulgens styani) endometrium.

Endometrial mesenchymal stem cells (eMSCs) are undifferentiated endometrial cells with self-renewal, multidirectional differentiation and high proliferation potential. Nowadays, eMSCs have been found in a few species, but it has never been reported in endangered wild animals, especially the red panda. In this study, we successfully isolated and characterized the eMSCs derived from red panda. Red panda eMSCs were fibroblast-like, had a strong proliferative potential and a stable chromosome number. Pluripotency genes including Klf4, Sox2 and Thy1 were highly expressed in eMSCs. Besides, cultured eMSCs were positive for MSC markers CD44, CD49f and CD105 and negative for endothelial cell marker CD31 and haematopoietic cell marker CD34. Moreover, no reference RNA-seq was used to analyse the eMSCs transcriptional expression profile and key pathways. Compared with skin fibroblast cell group, 9104 differentially expressed genes (DEGs) were identified, among which are 5034 genes upregulated, 4070 genes downregulated and the top 20 enrichment pathways of DEGs in Gene Ontology (GO) and the Kyoto Encyclopedia of Genes Genomes (KEGG) mainly associated with G-protein coupled receptor signalling pathway, carbohydrate derivative binding, nucleoside binding, ribosome biogenesis, cell cycle, DNA replication, Ras signalling pathway and purine metabolism. Among the DEGs, some representative genes about promoting MSCs differentiation and proliferation were upregulated and promoting fibroblasts proliferation were downregulated in eMSCs group. Red panda eMSCs also had multiple differentiation ability and could differentiate into adipocytes, chondrocytes and hepatocytes. In conclusion, we, for the first time, isolated and characterized the red panda eMSCs with ability of multiplication and multilineage differentiation in vitro. The new multipotential stem cell could be beneficial not only for the germ plasm resources conservation of red panda, but also for basic or pre-clinical studies in the future.

Chromosome numbers and heterochromatin variation in introgressed and non-introgressed populations ofEpidendrum(Orchidaceae: Epidendroideae): interspecific transfers of heterochromatin lead to divergent variable karyotypes in the parental populations

AbstractSome groups in Epidendrum have stable chromosome numbers, whereas the species of Epidendrum subgenus Amphiglottium exhibit high levels of chromosome number variability and other genomic alterations. Polyploidy and dysploidy have both been invoked to explain chromosome number variation in the subgenus, but little is known about what is driving the high frequency of chromosome modification within some species in this group. To test whether hybridization and introgression are involved, we use fluorochrome staining to evaluate the chromosome numbers and heterochromatin bands in E. subgenus Amphiglottium, including individual parental genotypes from introgressed and non-introgressed populations. Two main types of heterochromatin were observed forming CMA and DAPI bands in Epidendrum spp. B chromosomes were identified in some individuals. In non-introgressed populations, E. secundum has three cytotypes, 2n = 28, 56 and 84, found in different parts of its geographical range and a small number of DAPI bands. In introgressed populations of E. secundum, there was dysploid variation among individuals that were morphologically typical parental plants, and in one introgressed population a high number of DAPI bands was observed in what appeared on morphological grounds to be pure parental individuals. Our data corroborate the hypothesis that hybridization and introgression play a role in generating chromosome variation (number and form) and heterochromatin diversification in E. subgenus Amphiglottium.

High chromosomal mobility of rDNA clusters in holocentric chromosomes of Triatominae, vectors of Chagas disease (Hemiptera-Reduviidae).

The subfamily Triatominae (Hemiptera-Reduviidae) includes more than 150 blood-sucking species, potential vectors of the protozoan Trypanosoma cruzi, causative agent of Chagas disease. A distinctive cytogenetic characteristic of this group is the presence of extremely stable chromosome numbers. Unexpectedly, the analyses of the chromosomal location of ribosomal gene clusters and other repetitive sequences place Triatominae as a significantly diverse hemipteran subfamily. Here, we advance the understanding of Triatominae chromosomal evolution through the analysis of the 45S rDNA cluster chromosomal location in 92 Triatominae species. We found the 45S rDNA clusters in one to four loci per haploid genome with different chromosomal patterns: On one or two autosomes, on one, two or three sex chromosomes, on the X chromosome plus one to three autosomes. The movement of 45S rDNA clusters is discussed in an evolutionary context. Our results illustrate that rDNA mobility has been relatively common in the past and in recent evolutionary history of the group. The high frequency of rDNA patterns involving autosomes and sex chromosomes among closely related species could affect genetic recombination and the viability of hybrid populations, which suggests that the mobility of rDNA clusters could be a driver of species diversification.

Diversity of repetitive sequences within compact genomes of Phaseolus L. beans and allied genera Cajanus L. and Vigna Savi.

Repetitive sequences are ubiquitous and fast-evolving elements responsible for size variation and large-scale organization of plant genomes. Within tribe Phaseoleae (Fabaceae), some genera, such as Phaseolus, Vigna, and Cajanus, show small genome and mostly stable chromosome number. Here, we applied a combined computational and cytological approach to study the organization and diversification of repetitive elements in some species of these genera. Sequences were classified in terms of type and repetitiveness and the most abundant were mapped to chromosomes. We identified long terminal repeat (LTR) retrotransposons, especially Ogre and Chromovirus elements, making up most of genomes, other than P. acutifolius and Vigna species. Satellite DNAs (SatDNAs) were less representative, but highly diverse among species, showing a clear phylogenetic relationship. In situ localization revealed preferential location at pericentromeres and centromeres for both types of sequences, suggesting a heterogeneous composition, especially for centromeres. Few elements showed subterminal accumulation. Copy number variation among chromosomes within and among species was observed for all nine identified SatDNAs. Altogether, our data pointed two main elements (Ty3/Gypsy retrotransponsons and SatDNAs) to the diversification on the repetitive landscape in Phaseoleae, with a typical set of repeats in each species. The high turnover of these sequences, however, did not affect total genome size.

Genome size variation at constant chromosome number is not correlated with repetitive DNA dynamism in Anacyclus (Asteraceae).

Changes in the amount of repetitive DNA (dispersed and tandem repeats) are considered the main contributors to genome size variation across plant species in the absence of polyploidy. However, the study of repeatome dynamism in groups showing contrasting genomic features and complex evolutionary histories is needed to determine whether other processes underlying genome size variation may have been overlooked. The main aim here was to elucidate which mechanism best explains genome size evolution in Anacyclus (Asteraceae). Using data from Illumina sequencing, we analysed the repetitive DNA in all species of Anacyclus, a genus with a reticulate evolutionary history, which displays significant genome size and karyotype diversity albeit presenting a stable chromosome number. By reconstructing ancestral genome size values, we inferred independent episodes of genome size expansions and contractions during the evolution of the genus. However, analysis of the repeatome revealed a similar DNA repeat composition across species, both qualitative and quantitative. Using comparative methods to study repeatome dynamics in the genus, we found no evidence for repeat activity causing genome size variation among species. Our results, combined with previous cytogenetic data, suggest that genome size differences in Anacyclus are probably related to chromosome rearrangements involving losses or gains of chromosome fragments, possibly associated with homoploid hybridization. These could represent balanced rearrangements that do not disrupt gene dosage in merged genomes, for example via chromosome segment exchanges.

Precise transfers of genes for high grain iron and zinc from wheat-Aegilops substitution lines into wheat through pollen irradiation

Nearly 2 billion people worldwide are suffering from iron (Fe) deficiency anemia and zinc (Zn) deficiency. The available elite bread wheat cultivars have inherently low grain micronutrient content. Biofortification for grain Fe and Zn content is one of the most feasible and cost-effective approach for combating widespread deficiency of the micronutrients. QTL controlling high grain Fe and Zn have been mapped on groups 2 and 7 chromosomes of Triticeae. The present study was initiated for precise transfers of genes for high grain Fe and Zn on group 2 and 7 chromosomes of wheat-Aegilops substitution lines to wheat cultivars using pollen radiation hybridization. The pollen radiation hybrids (PRH1) derived from 1.75 krad irradiated spikes showed the presence of univalents and multivalents in meiotic metaphase-I indicating the effectiveness of radiation dose. In the advanced generation PRH5, the plants selected with stable chromosome number and high grain Fe and Zn content were analyzed with wheat groups 2 and 7 chromosome specific intron targeted amplified polymorphism (ITAP) markers of the metal homeostasis genes to monitor the transfers of alien genes from the substituted Aegilops chromosomes. The group 2 chromosome derivatives showed the presence of NAS2, FRO2, VIT1, and ZIP2 Aegilops genes whereas the group 7 derivatives had YSL15, NAM, NRAMP5, IRO3, and IRT2 Aegilops genes. The pollen radiation hybrids of both the groups 2 and 7 chromosomes showed more than 30% increase in grain Fe and Zn content with improved yield than the elite wheat cultivar PBW343 LrP indicating small and compensating transfers of metal homeostasis genes of Aegilops into wheat.

Cytotaxonomy of Allium (Amaryllidaceae) subgenera Cyathophora and Amerallium sect. Bromatorrhiza

In the present study, we examined the karyotype data of subg. Cyathophora and sect. Bromatorrhiza, to determine some disputed karyotypes (e.g., A. spicatum and A. fasciculatum), and further to estimate the karyotype evolution along their phylogenetic frameworks. Our results revealed a fairly stable basic chromosome number (x = 8) in subg. Cyathophora, and we therefore revised x = 8 as the basic chromosome number of A. spicatum, rather than x = 10 mostly due to misidentifications concerning A. fasciculatum. The karyotype asymmetry analyses for subg. Cyathophora indicated that, the karyotype evolution for diploid species showing a high karyotype similarity was mainly due to intrachromosomal changes, while the interchromosomal changes were linked to the evolution of tetraploid populations. However, indeed different dysploid basic chromosome numbers (x = 7, 10, 11) and greatly different karyotype patterns occurred in sect. Bromatorrhiza, corresponding to the subsections revealed by molecular evidence. The combined evidence suggested that species with x = 11 compose a segmental allotriploid complex. It was also indicated that karyotype pattern of polyploids usually is closely related with their diploid progenitors.

Introgressing Subgenome Components from Brassica rapa and B. carinata to B. juncea for Broadening Its Genetic Base and Exploring Intersubgenomic Heterosis.

Brassica juncea (AjAjBjBj), is an allotetraploid that arose from two diploid species, B. rapa (ArAr) and B. nigra (BnBn). It is an old oilseed crop with unique favorable traits, but the genetic improvement on this species is limited. We developed an approach to broaden its genetic base within several generations by intensive selection. The Ar subgenome from the Asian oil crop B. rapa (ArAr) and the Bc subgenome from the African oil crop B. carinata (BcBcCcCc) were combined in a synthesized allohexaploid (ArArBcBcCcCc), which was crossed with traditional B. juncea to generate pentaploid F1 hybrids (ArAjBcBjCc), with subsequent self-pollination to obtain newly synthesized B. juncea (Ar/jAr/jBc/jBc/j). After intensive cytological screening and phenotypic selection of fertility and agronomic traits, a population of new-type B. juncea was obtained and was found to be genetically stable at the F6 generation. The new-type B. juncea possesses good fertility and rich genetic diversity and is distinctly divergent but not isolated from traditional B. juncea, as revealed by population genetic analysis with molecular markers. More than half of its genome was modified, showing exotic introgression and novel variation. In addition to the improvement in some traits of the new-type B. juncea lines, a considerable potential for heterosis was observed in inter-subgenomic hybrids between new-type B. juncea lines and traditional B. juncea accessions. The new-type B. juncea exhibited a stable chromosome number and a novel genome composition through multiple generations, providing insight into how to significantly broaden the genetic base of crops with subgenome introgression from their related species and the potential of exploring inter-subgenomic heterosis for hybrid breeding.

Cytological details of Luffa cylindrica (L.)M.Roem. a meiotically disturbed diploid

Present work embodies cytological analysis of Luffa cylindrica (L.)M.Roem., an economically important Cucurbit. L. cylindrica is found only under cultivation and has a diploid chromosome number of 2n = 26. Ten cultivars of this species collected from different parts of Jammu province of J&K state (India) were studied for their reproductive features, meiotic behaviour and somatic chromosome complement. All of them displayed some anomalies during meiosis that resulted in low pollen viability. This undesirable trait was however compensated by bold reproductive features and efficient pollen transfer in the species leading to high fruit and seed set. Mitotic studies revealed L. cylindrica to have stable diploid chromosome number with a primitive and little evolved karyotype. Presence of multivalents and erratic anaphase segregation during meiosis however point towards some structural rearrangements in the chromosomes which are difficult to detect because of small size of chromosomes and little variation in their size.

Chinese cabbage (Brassicarapa ssp. pekinensis) \u2013 a valuable source of resistance to clubroot (Plasmodiophora brassicae)

Clubroot, caused by the protozoan parasite Plasmodiophora brassicae Woronin, is one of the most damaging diseases of Brassica napus worldwide. Resistant plant material is valuable for cultivation in all areas of high incidence of the disease and intensive growth of oilseed rape. We have evaluated clubroot resistance, plant morphology and seed quality in 15 lines of an F4 generation and selected six lines of F5 generation of interspecific hybrids obtained from a cross between a male sterile line of B. napus ‘MS8’, selected from resynthesized oilseed rape (B. rapa ssp. chinensis × B. oleracea var. gemmifera) and an ecotype of B. rapa ssp. pekinensis. Clubroot resistance was evaluated using a bioassay with P1-P5 pathotypes of P. brassicae (according to the classification of Somé et al. 1996). The resistance to the pathotype P1 was successfully fixed in the F5 generation, and improved in some lines in respect to the pathotypes P2-P4. The resistance to P1 and the other tested pathotypes was not linked. Characterization of plant material included recent techniques of FISH and BAC-FISH with a special focus on the analysis of ribosomal DNA (rDNA) of selected individuals. Two hybrid lines combined high levels of resistance with appropriate plant morphology, good seed quality traits and a stable chromosome number and arrangement. Recent techniques of ‘chromosome painting’ provided good insight into chromosome organization in the hybrids obtained, and offered opportunities of further improvement of the breeding process.

Karyotype analysis on 11 species of the genus Clematis

In order to explore the karyotype and evolutionary trend of Clematis and provide taxonomically useful data, the chromosome number, the number and position of satellites, the karyotype formulae, the karyotype, arm ratio, relative length centromeric index, and the index of the karyotype asymmetry of 11 species of the genus Clematis were studied. All the analyzed species showed the same stable chromosome number (2n = 2x = 16) and basic chromosome number 8. Clematis karyotypes are composed by metacentric, submetacentric, and terminal centromeric chromosomes. Clematis lanuginosa, C. otophora, C. lasiandra, C. shenlungchiaensis, C. florida var. plena, C. fusca var. violacea, C. crispa, and C. viticella belong to Type 2A, a very symmetric and plesiomorphic type. Clematis henryi, C. integrifolia, and C. japonaca belong to Type 2B, which is apomorphic relative to the other group. The 11 species of Clematis are different in karyotype parameters providing data for the taxonomy of the genus.

A comparative study of genome organization and inferences for the systematics of two large bushcricket genera of the tribe Barbitistini (Orthoptera: Tettigoniidae: Phaneropterinae)

BackgroundPoecilimon and Isophya are the largest genera of the tribe Barbitistini and among the most systematically complicated and evolutionarily intriguing groups of Palearctic tettigoniids. We examined the genomic organization of 79 taxa with a stable chromosome number using classical (C–banding, silver and fluorochrome staining) and molecular (fluorescence in situ hybridization with 18S rDNA and (TTAGG) n telomeric probes) cytogenetic techniques. These tools were employed to establish genetic organization and differences or similarities between genera or species within the same genus and determine if cytogenetic markers can be used for identifying some taxonomic groups of species.ResultsDifferences between the karyotypes of the studied genera include some general changes in the morphology of the X chromosome in Isophya (in contrast to Poecilimon). The number of major rDNA clusters per haploid genome divided Poecilimon into two main almost equal groups (with either one or two clusters), while two rDNA clusters predominated in Isophya. In both genera, rDNA loci were preferentially located in the paracentromeric region of the autosomes and rarely in the sex chromosomes. Our results demonstrate a coincidence between the location of rDNA loci and active NORs and GC-rich heterochromatin regions. The C/DAPI/CMA3 bands observed in most Poecilimon chromosomes suggest the presence of more families of repetitive DNA sequences as compared to the heterochromatin patterns in Isophya.ConclusionsThe results show both differences and similarities in genome organization among species of the same genus and between genera. Previous views on the systematics and phylogenetic grouping of certain lineages are discussed in light of the present cytogenetic results. In some cases, variation of chromosome markers was observed to correspond with variation in other evolutionary traits, which is related to the processes of ongoing speciation and hybridization in zones of secondary contact. It was concluded that the physical mapping of rDNA sequences and heterochromatin may be used as an additional marker for understanding interspecific relationships in these groups and their routes of speciation.

A study of chromosome numbers of Petasites frigidus (L.) Fries and Petasites radiatus (J. F. Gmel.) Toman (Asteraceae) of Altai, Russia

Petasites frigidus (L.) Fries had the stable chromosome number of 2n=60. However, P. radiatus (J. F. Gmel.) Toman had a mixoploidy since the majority of the mitotic metaphase cells showed 2n=86~90 (83% metaphase cells studied) and 2n=30 (14% metaphase cells studied). Numerous data on chromosome numbers of Petasites reported in various species of the genus in 1970’s to 1980’s commonly reported 2n=60 by several authors should be rechecked and determined again.