Dual-color FISH karyotype analyses using rDNAs in three Cucurbitaceae species

Dual-color fluorescence in situ hybridization (FISH) analysis of three Cucurbitaceae species from different genera was conducted using 5S and 45S rDNA probes. In Benincasa hispida (Thunb.) Cogn. (2n=24), the 45S rDNA probe hybridized on two chromosomes, one in the short arm of a medium-sized metacentric chromosome and another at the satellite of a chromosome. The 5S rDNA hybridized at a site proximal to the centromere of the same short arm of the 45S rRNA gene locus that occupied almost the entire short arm. For Citrullus lanatus (Thunb.) Matsum & Nakai (2n=22), the 45S rDNA probe hybridized at sites in the short arms of two chromosomes and the 5S rDNA probe was co-localized with the 45S rRNA locus at the region proximal to the centromere in one chromosome. The 45S rRNA loci occupied almost all of the short arms in both chromosomes. In Cucurbita moschata Duch. (2n=40), the 45S rDNA probe hybridized in five chromosomes in which the 45S rRNA genes occupied almost two-thirds of the chromosomes in two large chromosomes and the entire short arm of a medium-sized chromosome. Two other loci were present in two medium-sized chromosomes, one in the proximal region in the short arm of a chromosome and another at the tip of the long arm of a chromosome. Chromosomes of B. hispida were relatively larger than those of the other two species. The karyotype of B. hispida is composed of two metacentrics and 10 submetacentrics, while that of C. lanatus is composed of seven metacentrics and four submetacentrics and that of C. moschata is composed of 18 metacentrics and two submetacentrics. Comparative chromosome evolution among the three Cucurbitaceae species was attempted using the karyotypes and the chromosomal distribution patterns of the 5S and 45S rDNAs. The results presented herein will be useful in elucidating the phylogenetic relationships among Cucurbitaceae species, and will provide basic data for their breeding programs.     

Karyologic diversification and phylogenetic relationships of the genus<Emphasis Type="Italic">Thalpomys</Emphasis> (Rodentia,Sigmodontinae)

We describe the karyotype ofThalpomys species, from different Brazilian localities of the Cerrado.Thalpomys cerradensis Herskovitz, 1990 showed 2n=36, FN=34 andT. lasiotis Thomas, 1916 2n=38, FN=38. Comparisons of G-band karyotypes showed evident inter-specific homologies indicating that their chromosome complements could be derived from one another by two presumed rearrangements. Both species showed pericentromeric C-band regions in almost all chromosomes but a comparison with CMA3/DA/DAPI staining indicated that the molecular content of heterochromatic regions was different.T. lasiotis specimens from two different localities differed in the morphology of the X chromosome due to the presence of a short heterochromatic arm. These chromosome types are apparently fixed in each population rather than maintained as a polymorphic variation. Phylogenetic analyses supported the monophyly of the genusThalpomys but was not capable of elucidating its phylogenetic relationship to other Akodontini rodents. These analyses also showed inter-individual variation inT. lasiotis, even within a given population. Phylogenetic analyses placedT. lasiotis specimens with different karyotypes in different monophyletic branches. Molecular and karyologic data confirmed the identity of the genusThalpomys.     

Latitudinal clines in the grasshopper Dichroplus elongatus: Coevolution of the A genome and B chromosomes?

Argentine populations of Dichroplus elongatus (Orthoptera: Acrididae) are polymorphic for B chromosomes. Previous studies showed that B chromosomes affect body size and some fitness components in Northwestern populations. We studied phenotype and B′s variation patterns along a latitudinal cline as well as the relationship between karyotype and body size related traits in 17 populations from East. Body size related traits showed a ‘saw tooth’ pattern of variation being small at low and high latitudes and large at intermediate latitudes in most of the analysed populations. Analyses of variance and principal components demonstrated that in most analysed populations B carrier males are associated with a decrease in body size related traits with respect to individuals with standard karyotype. Accordingly with the relationship between karyotype and body size, an opposite pattern of latitudinal variation in the frequencies of B′s with respect to body size variation was observed in this area. i.e. smaller individuals tend to have a higher frequency of B chromosomes. The comparison of the differentiation of both karyotype and body size traits with molecular neutral markers demonstrated the relative importance of selection moulding chromosome and phenotype variation. The observed pattern of phenotypic variation is likely to be the result of local adaptation to season length along the latitudinal gradient. The observed contrary pattern of B′s clinal variation may reflect the population ability to maintain this chromosome in relation to the local adaptation. The available evidence indicates that the distribution of B chromosome frequency was shaped by selective factors.     

Genetic Variability in the Yellow-Necked Field Mouse (<Emphasis Type="Italic">Sylvaemus flavicollis</Emphasis> Melch., 1834, Muridae,Rodentia) at the Eastern Border of the Range

The first characterization of the genetic variability in populations of S. flavicollis on the eastern border of the range is presented. Seven individuals from the most northeastern habitat of the species (Middle Urals) were karotyped. No deviations from the standard chromosome set, either by the chromosome number or morphology, were revealed. Analysis of the mtDNA cytochrome b gene sequences (1133 bp) in 44 individuals from five populations on the eastern border of the species range (Middle and Southern Urals) resulted in identification of 17 haplotypes. All haplotypes were new and not found earlier in other parts of the species range. The genetic diversity indices and analysis of the demographic and genetic structure indicate a relatively recent origin of the populations under study as a result of rapid expansion. Phylogenetic analysis (97 haplotypes, including the GenBank data) showed that all haplotypes described at the eastern border of the range belonged to the same phylogroup distributed in the Balkan region, Northern and Eastern Europe, and Russia (Samara oblast). Close relationships between the examined populations and the populations from the northern part of the species range in Eastern Europe was demonstrated.     

Polymorphism and mosaicism of B chromosome number in Korean field mouse <Emphasis Type="Italic">Apodemus peninsulae</Emphasis> (Rodentia) in the Russian Far East

A karyotype analysis of the Apodemus peninsulae (n = 355) from 41 trapping points from the Russian Far East has allowed us to identify B chromosomes in 87.9% of the animals, 61.7% of which are mosaics. Different levels of variability in the B chromosome numbers have been studied, including both the inter- and intrapopulational, as well as intraindividual variability (mosaicism). It was found that the frequencies of the occurrence of individuals with B chromosomes and mosaicism between different population samples were not constant. The range of the modal B chromosome number variability and variation of the xB index (zero to four; on average, the xB amounted to 1.67) were studied for the first time in different samples and populations of this species. Individuals with the predominant numbers of B chromosome (as a rule, zero to two) were revealed in both groups of animals (with stable and mosaic karyotypes), but the frequency was different in geographical regions. The spectra of B chromosome variability were wider in mosaics (zero to seven) compared to animals with stable karyotypes (zero to four). The importance of this for species of the high frequency of individuals with B chromosomes and with mosaicism has been discussed. The adaptive role of the low number of B chromosomes (one to two), as well as the imbalance of the B chromosome system for the species as a whole is assumed.     

Investigation of karyotypic composition and evolution in <Emphasis Type="Italic">Lilium</Emphasis> species belonging to the section martagon

Analyzing chromosomal traits is one of the pragmatic ways to establish evolutionary and genetic database of plants that has complicated phylogenetic system. There are some conflicts on the exact phylogeny and evolutionary pathway of Lilium, and section martagon is the most complicated part among them. In this study, chromosomal traits of martagon lily species are described. All martagon lilies were analyzed with FISH (Fluorescence in situ hybridization) technique, followed by detailed karyotyping. Each species showed 2n = 2x = 24 of chromosome complement. Size of chromosomes ranged from 451.04 to 680.06 µm. 5S and 45S ribosomal DNA, general molecular markers in modern evolutionary research were used as probe in this study. Variation in rDNA loci and chromosome translocation were observed in Lilium hansonii; the highest number of 45S rDNA loci was detected in Lilium hansonii, followed by other martagon lilies, in similar locations but with differences, and chromosome translocation was observed from one individual of Lilium hansonii. Additionally, Lilium tsingtauense from Jeju-do Island, Korea was detected with two extra chromosomes. These kind of genetic variations through karyotyping indicate ongoing genetic variations in martagon lilies. In this study, precise analysis of chromosome traits in Lilium species belonging to section martagonperformed to contribute to better comprehension of the evolutionary pathway and establishment of cytogenetic database for further plant breeding research.     

Biogeographic distribution of polyploidy and B chromosomes in the apomictic Boechera holboellii complex

The Boechera holboellii complex comprises B. holboellii and B. drummondii, both of which can reproduce through sex or apomixis. Sexuality is associated with diploid individuals, whereas apomictic individuals are diploid or triploid and may additionally have B chromosomes. Using flow cytometry and karyotype analysis, we have shown that B chromosomes (a) occur in both diploid and triploid apomictic B. holboellii, (b) may occur in triploid B. drummondii, and (c) are dispensable for the plant. Both diploid and triploid karyotypes are found in multiple chloroplast haplotypes of both species, suggesting that triploid forms have originated multiple times during the evolution of this complex. B chromosome carriers are found in geographically and genetically distinct populations, but it is unknown whether the extra chromosomes are shared by common descent (single origin) or have originated via introgressive hybridization and repeated transitions from diploidy to triploidy. Diploid plants containing the Bs reproduce apomictically, suggesting that the supernumerary elements are associated with apomixis. Finally, our analyses of pollen size and viability suggest that irregular chromosome segregation in some triploid lineages may lead to the generation of diploid individuals which carry the B chromosomes.     

Multiple Pleistocene refugia and post‐glacial colonization in the European chub (Squalius cephalus) revealed by combined use of nuclear and mitochondrial markers

Aim To analyse patterns of nuclear and mitochondrial genetic variation in the European chub, Squalius cephalus (Linnaeus, 1758), in order to understand the evolutionary history of this species and to test biogeographical hypotheses for the existence of co‐distributed European freshwater fish species. Location Rivers in Europe (Finland, Poland, Czech Republic, France, Bulgaria, Spain, Italy). Methods We genotyped 12 polymorphic microsatellite markers derived from 310 individuals collected from across the distribution of S. cephalus in Europe (including a total of 15 populations) and sequenced mitochondrial DNA (mtDNA) from a subset of 75 individuals. Sequences of mtDNA cytochrome b were analysed using both phylogenetic (median‐joining networks) and population genetic methods (tests for demographic history, mismatch distributions, Bayesian coalescent analysis). Geographical structure in microsatellite loci was examined using a distance method (F_ST), factorial correspondence analysis (FCA) and a Bayesian clustering method (structure ). Results The mtDNA network showed a clear split into four different haplogroup lineages: Western (separated into Atlantic and Danubian sublineages), Eastern, Aegean (occurring in two distinct sublineages in the Balkans and in Spain) and Adriatic. Our results indicate recent population expansion in the Eastern and Western Atlantic lineages and the admixture of two previously separate sublineages (Atlantic and Danubian) in the Western lineage. Bayesian structure analysis as well as FCA results roughly corresponded to the mtDNA‐based structure, separating the sampled individuals into almost non‐overlapping groups. Main conclusions Our results support hypotheses suggesting origins of extant lineages of freshwater fishes in multiple refugia and the subsequent post‐glacial colonization of Europe via different routes. We confirmed the previously proposed two‐step expansion scenario from the Danube refuge, the existence of a secondary (Atlantic) refuge during the last glaciation (probably in the Rhone River) and population expansion of this lineage. Conspicuous divergences among Mediterranean populations reflect their different origin, as well as their low contribution to the recent genetic pool of chub in central Europe.     

Karyology and karyotype analysis of diploid freshwater planarian populations of the Dugesia gonocephala group (Platyhelminthes,Tricladida) found in Sardinia

Karyology and karyotype analysis were carried out on freshwater planarian populations of the Dugesia gonocephala group. The strains studied were all diploid with chromosomic number 2n = 16; n = 8. They came from 12 sites mainly localized on the west of the island of Sardinia. Three karyotypes indicated with the letters A, B and C were found in which eight homomorphic pairs of chromosomes were easily identified. In karyotype A all chromosomes are metacentric. Ten populations of the twelve examined showed this karyotype which appears to be the most common. In karyotype B the seventh pair of chromosomes is submetacentric. This karyotype is quite common having been previously found in another eight Sardinian localities. Karyotype C differs from the others in having submetacentric third and seventh pairs of the chromosome complement. It was found in only one locality. The differences observed between these three karyotypes could be interpreted either as sign of differentiation at species level, or as an intraspecific variation due to chromosome mutations (pericentric inversions). This revised version was published online in July 2006 with corrections to the Cover Date.     

Features of the genetic structure of the earthworms <Emphasis Type="Italic">Aporrectodea</Emphasis> (Superspecies) <Emphasis Type="Italic">Caliginosa</Emphasis> (Oligochaeta: Lumbricidae) complex in Ukraine

An investigation of the genetic structure of the Aporrectodea caliginosa-A. trapezoids diploidpolyploid complex of earthworms found in the Ukraine is performed by means of biochemical genetic marking with respect to six loci (Aat, Es-1,-2,-3, and-4, and Mdh) and karyotyping. All 646 individuals from 21 samples are analyzed at the biochemical gene level and karyotype samples are obtained from 70 specimens. As a result, diploid amphimictic A. caliginosa individuals (2n = 36), which form panmictic populations, and triploid (2n = 54) A. trapezoides individuals, represented by 19 hypothetical clones discovered in the course of an analysis of 157 specimens, are clearly differentiated. A clear trend towards dominance of the triploid forms in the steppe zone of Ukraine is discovered. Here they represent roughly 70% as against 12% of all A. (superspecies) caliginosa individuals in the northern forest regions. Based on the stated nature of the heterozygosity of the loci studied and the behavior of the chromosomes in meiosis, it may be claimed that the cloned forms are allotriploids, formed as a result of hybridization of a series of related forms, which, judging from the allelic pools, does not include amphimictic species that now inhabit the territory of Ukraine. That is, either the apomictic clones of A. trapezoides lack a local origin and their appearance among the fauna of Ukraine is a consequence of settlement in arid steppe regions that are unfavorable for earthworms or, on the other hand, amphimictic A. caliginosa is an invasive species.     

Population structure of North Atlantic and North Pacific sei whales (<Emphasis Type="Italic">Balaenoptera borealis</Emphasis>) inferred from mitochondrial control region DNA sequences and microsatellite genotypes

Currently, three stocks of sei whales (Balaenoptera borealis) are defined in the North Atlantic; the Nova Scotian, Iceland-Denmark Strait and Eastern North Atlantic stocks, which are mainly based upon historical catch and sighting data. We analyzed mitochondrial control region DNA (mtDNA) sequences and genotypes from 7 to 11 microsatellite loci in 87 samples from three sites in the North Atlantic; Iceland, the Gulf of Maine and the Azores, and compared against the North Pacific using 489 previously published samples. No statistically significant deviations from homogeneity were detected among the North Atlantic samples at mtDNA or microsatellite loci. The genealogy estimated from the mtDNA sequences revealed a clear division of the haplotypes into a North Atlantic and a North Pacific clade, with the exception of one haplotype detected in a single sample from the Azores, which was included in the North Pacific clade. Significant genetic divergence between the North Atlantic and North Pacific Oceans was detected (mtDNA Φ_ST?=?0.72, microsatellite Weir and Cockerham’s ? = 0.20; p?<?0.001). The coalescent-based estimate of the population divergence time between the North Atlantic and North Pacific populations from the sequence variation among the mtDNA sequences was at 163,000 years ago. However, the inference was limited by an absence of samples from the Southern Hemisphere and uncertainty regarding mutation rates and generation times. The estimates of inter-oceanic migration rates were low (Nm at 0.007 into the North Pacific and at 0.248 in the opposite direction). Although estimates of genetic divergence among the current North Atlantic stocks were low and consistent with the extensive range of movement observed in satellite tagged sei whales, the high uncertainty of the genetic divergence estimates precludes rejection of multiple stocks in the North Atlantic.     

Cytogenetic analyses of eight species in the genus <Emphasis Type="Italic">Leptodactylus</Emphasis> Fitzinger, 1843 (Amphibia,Anura, Leptodactylidae), including a new diploid number and a karyotype with multiple translocations

Background

The karyotypes of Leptodactylus species usually consist of 22 bi-armed chromosomes, but morphological variations in some chromosomes and even differences in the 2n have been reported. To better understand the mechanisms responsible for these differences, eight species were analysed using classical and molecular cytogenetic techniques, including replication banding with BrdU incorporation.

Results

Distinct chromosome numbers were found: 2n = 22 in Leptodactylus chaquensis, L. labyrinthicus, L. pentadactylus, L. petersii, L. podicipinus, and L. rhodomystax; 2n = 20 in Leptodactylus sp. (aff. podicipinus); and 2n = 24 in L. marmoratus. Among the species with 2n = 22, only three had the same basic karyotype. Leptodactylus pentadactylus presented multiple translocations, L. petersii displayed chromosome morphological discrepancy, and L. podicipinus had four pairs of telocentric chromosomes. Replication banding was crucial for characterising this variability and for explaining the reduced 2n in Leptodactylus sp. (aff. podicipinus). Leptodactylus marmoratus had few chromosomes with a similar banding patterns to the 2n = 22 karyotypes. The majority of the species presented a single NOR-bearing pair, which was confirmed using Ag-impregnation and FISH with an rDNA probe. In general, the NOR-bearing chromosomes corresponded to chromosome 8, but NORs were found on chromosome 3 or 4 in some species. Leptodactylus marmoratus had NORs on chromosome pairs 6 and 8. The data from C-banding, fluorochrome staining, and FISH using the telomeric probe helped in characterising the repetitive sequences. Even though hybridisation did occur on the chromosome ends, telomere-like repetitive sequences outside of the telomere region were identified. Metaphase I cells from L. pentadactylus confirmed its complex karyotype constitution because 12 chromosomes appeared as ring-shaped chain in addition to five bivalents.

Conclusions

Species of Leptodactylus exhibited both major and minor karyotypic differences which were identified by classical and molecular cytogenetic techniques. Replication banding, which is a unique procedure that has been used to obtain longitudinal multiple band patterns in amphibian chromosomes, allowed us to outline the general mechanisms responsible for these karyotype differences. The findings also suggested that L. marmoratus, which was formerly included in the genus Adenomera, may have undergone great chromosomal repatterning.

     

Production of wheat-rye substitution lines based on winter rye cultivars with karyotype identification by means of C-banding,GISH, and SSR markers

The study presents a continuation of the research aimed at producing of wheat-rye substitution lines (2n = 42) based on the cross (Triticum aestivum L. × Secale sereale L.) × Triticum aestivum L., and using winter rye cultivars Vyatka and Vietnamskaya Mestnaya. In BC 1 F 5 two lines were identified, having karyotypes in which a pair of homologous wheat chromosomes was substituted by a homeologous pair of rye chromosomes. The chromosome composition of these lines was analyzed using C-banding, GISH, and SSR markers. It was demonstrated that karyotype of each line included a single pair of rye chromosomes and lacked wheat-rye translocations. The rye chromosomes were identified, and the chromosomes of wheat, at which the substitutions occurred, were determined. The lines generated by crosses with rye of Vyatka and Vietnamskaya Mestnaya cultivars were designated 1Rv(1A) and 5Rviet(5A), respectively. Chromosome identification and classification of the lines makes it possible to use them in breeding programs and genetic studies.     

Karyotype of the rare Johnston’s genet<Emphasis Type="Italic">Genetta johnstoni</Emphasis> (Viverridae) and a reassessment of chromosomal characterization among congeneric species

We present herein new data on karyotypes of members of the genusGenetta. G- and C-banded chromosomes of the Johnston’s genetGenetta johnstoni Pocock, 1908 (2n = 50 / FNa = 92) are described for the first time, and compared with those ofG. genetta (2n = 54 / FNa = 92). In addition, the standard karyotype ofG. maculata (2n = 52 / FNa = 96) was studied. A reassessment of taxonomic attribution of previously published material allowed us to characterize (2n, FNa, and chromosome morphology) the karyotypes of three genets, previously unknown (G. pardina, G. letabae andG. tigrina). Our results show that despite a rather low interspecific variability in 2n and FNa, all the species of genets (exceptG. pardina andG. maculata) appear differentiated when chromosomal morphology is taken into account. Although chromosomal banding data are limited, confrontation of G-band karyotypes with preliminary molecular phylogenetic results reveals that karyotypic evolution within the genusGenetta might involve various rearrangements like Robertsonian and tandem translocations, pericentric inversions, and centromere fissions; thus providing at least for some taxa a solid postzygotic isolation. Finally, our study suggests that cytogenetic analyses might constitute a useful tool for questioning interspecific boundaries, especially within the taxonomically debated complex of large-spotted genets.     

Karyological studies of Iranian <Emphasis Type="Italic">Allium</Emphasis> L. (Amaryllidaceae) species with focus on sect. <Emphasis Type="Italic">Acanthoprason</Emphasis>. 1. Mitotic chromosomes

Eighteen species and subspecies (34 accessions) of Allium sect. Acanthoprason and 11 species (17 accessions) belonging to other subgenera and sections of Allium were karyologically investigated and include first reports for 12 species. The examined plants of 47 accessions were diploid, three accessions of two species were tetraploid, and in the A. bisotunense accession, we found a mix of di- and triploid individuals. B chromosomes were found in 10 accessions. A basic chromosome number of x = 8 was confirmed for all investigated members of subg. Melanocrommyum and subg. Allium, and x = 9 for Allium tripedale of subg. Nectaroscordum. Idiograms were drawn for each accession, and metaphase images are presented illustrating observed chromosomal variations. Also, karyotype features and asymmetry parameters were calculated for all accessions. Chromosomal aberrations, e.g. aneuploid cells or loss of whole or parts of chromosome arms, were rarely observed. In general, the karyotypes showed low variation in inter- and intrachromosomal asymmetry especially inside of the taxonomic groups, though satellited chromosomes were good markers for subgenera and even specific for two studied sections of subg. Allium. Six different types of satellites were recognized, two of them were newly described: Type P was prevalent in subg. Melanocrommyum, and type O in sect. Codonoprasum. Statistical analyses were performed on five karyological parameters to test correct relationships and also to test previous grouping hypotheses. Although our data confirm distinct karyological characters for the subgenera investigated, the remarkable morphological diversity inside of subg. Melanocrommyum is not mirrored by striking karyological differences.     

Diversity and individuality of variants of the system of B chromosomes in mice <Emphasis Type="Italic">Apodemus peninsulae</Emphasis>

A complicated population system of B chromosomes has been revealed in the karyotypes of the East-Asian mouse Apodemus peninsulae over the whole range. Based on our previous data for mice from Altai, Siberia, Pribaikal’e, and Mongolia and on the results of the present work, we infer that most of animals studied (196 out of 312, or 63%) have an individual variant of the B chromosome system. Only three mice lacked B chromosomes. New data for 44 A. peninsulae mice caught in 2000–2005 in 16 localities of seven regions of Altai, Siberia, and Pribaikal’e showed that all of them had individual variants of the system of B chromosomes due to different combinations (from 2 to 18 B chromosomes) of five classes of B macro- and microchromosomes.     

Mapping of five human chromosome 19 DNA markers to owl monkey chromosomes.

Hybridization of DNA from three panels of karyotypically distinct owl monkey x rodent somatic cell hybrids with human DNA probes resulted in the syntenic assignments of INSR-LDLR-TGFB1-APOE-D19S8 to owl monkey chromosome 25 of karyotype VI (2n = 49/50), INSR-LDLR-TGFB1-D19S8 to chromosome 2 of karyotype II (2n = 54), and INSR-APOE to chromosome 2 of karyotype V (2n = 46). The APOE and D19S8 loci are on adjacent regions proximal to the centromere of chromosomes 25q (K-VI) and 2p (K-II), as determined by in situ chromosomal hybridization analysis. These findings support our previous proposals on (1) the homology of these chromosomes of three owl monkey karyotypes, (2) the evolutionary derivation of chromosome 2 of karyotypes II and V as the result of two separate centric fusion events, and (3) the likelihood that owl monkey chromosome 25 (K-VI) (and its homologs) is a conserved genetic homoeolog of human chromosome 19.     

Karyotype variation is indicative of subgenomic and ecotypic differentiation in switchgrass

ABSTRACT: BACKGROUND: Karyotypes can provide information about taxonomic relationships, genetic aberrations, and the evolutionary origins of species. However, differentiation of the tiny chromosomes of switchgrass (Panicum virgatum L.) and creation of a standard karyotype for this bioenergy crop has not been accomplished due to lack of distinguishing features and polyploidy. RESULTS: A cytogenetic study was conducted on a dihaploid individual (2n=2X=18) of switchgrass to establish a chromosome karyotype. Size differences, condensation patterns, and arm-length ratios were used as identifying features and fluorescence in-situ hybridization (FISH) assigned 5S and 45S rDNA loci to chromosomes 7 and 2 respectively. Both a maize CentC and a native switchgrass centromeric repeat (PviCentC) that shared 73% sequence identity demonstrated a strong signal on chromosome 3. However, only the PviCentC probe labeled the centromeres of all chromosomes. Unexpected PviCentC and 5S rDNA hybidization patterns were consistent with severe reduction or total deletion of these repeats in one subgenome. These patterns were maintained in tetraploid and octoploid individuals. The 45S rDNA repeat produced the expected number of loci in dihaploid, tetraploid and octoploid individuals. Differences observed at the 5S rDNA loci between the upland and lowland ecotypes of switchgrass provided a basis for distinguishing these subpopulations. CONCLUSION: Collectively, these results provide a quantitative karyotype of switchgrass chromosomes. FISH analyses indicate genetic divergence between subgenomes and allow for the classification of switchgrass plants belonging to divergent genetic pools. Furthermore, the karyotype structure and cytogenetic analysis of switchgrass provides a framework for future genetic and genomic studies.     

Genetic structure of the populations of <Emphasis Type="Italic">Dactylorhiza ochroleuca</Emphasis> and <Emphasis Type="Italic">D. incarnata</Emphasis> (Orchidaceae) in the area of their joint growth in Russia and Belarus

We carried out an allozyme analysis to investigate polymorphism and genetic structure of the populations of D. incarnata and D. ochroleuca in regions of their joint growth in Russia and Belarus. We found that D. ochroleuca individuals in the populations of the Urals and Siberia, which are distant fragments from the main range of the species, do not differ significantly from individuals within the main part of the area (Belarus) on the basis of the allelic composition of eight gene loci. We revealed that D. ochroleuca and D. incarnata are differentiated by different alleles of the GDH locus. Thus, we established a genetic marker suitable to distinguish these closely related taxa. In addition to the GDH locus, D. ochroleuca and D. incarnata in the places of their joint growth, differ in the allelic structure of the PGI and NADHD loci. D. incarnata from the Urals and Siberia were polymorphic for both loci, and individuals from Belarus were polymorphic for one locus (PGI). In contrast, all D. ochroleuca individuals growing in sympatric populations with polymorphic D. incarnata were homozygous for the same alleles. Thus, comparison of the genetic structure of D. ochroleuca and D. incarnata points to the existence of a genetic isolation and a functioning isolation mechanism even under conditions of their joint growth. We found that the GDH locus in D. incarnata is polymorphic only in populations which grow together with D. ochroleuca, with exception a few examples. Thus, we conclude that variability of the GDH locus in D. incarnata is associated with hybridization with D. ochroleuca.