Giemsa C-banding patterns in Aedes (Stegomyia) mosquitoes

Chromosomes from gonads of 14–24 h old pupae of nine species of Stegomyia mosquitoes have been examined using the Giemsa C-banding technique. The species studied were Aedes albopictus, A. polynesienis, A. scutellaris, A. alcasidi, A. seatoi, A. pseudalbopictus, A. melallicus, A. annandalei and A. vittatus. The diploid chromosome number of all species is six. All species possess C-bands in the centromeric regions of each of the three pairs of chromosomes. Besides, an intercalary C-band is present on the female determining (=m) chromosome but absent from the male—determining (= M) chromosome of all species except A. vittatus. In A. vittatus, the m and M chromosomes possess a terminal C-band. Thus, the nine species of Aedes analysed showed two distinct patterns of C-banding. —The evolution of heterochromatin patterns in various species is also discussed. The Giemsa C-banding technique should prove useful in studies of chromosomal speciation in culicine mosquitoes.     

Identification of C-banded chromosomes in meiosis and the analysis of nucleolar activity in Avena byzantina C. Koch cv ‘Kanota’

Summary The Giemsa C-banding technique was used to identify individual meiotic and somatic chromosomes in 21 monosomic lines of Avena byzantina C. Koch cv Kanota (genome designation AACCDD). The hexaploid complement is composed of three sets of seven chromosome pairs. The heterochromatin in the putative diploid progenitors is located at the telomeres (genome A), at the centromeric and interstitial regions (genome C), or more evenly spread throughout the set (genome D). Comparisons based on C-banding between A. byzantina and its diploid progenitor species allowed us to allocate individual chromosomes into specific genomes. The C-banding technique may be useful for interspecific chromosome pairing analyses. Nucleolar activity and competition were studied using a silver-staining procedure. Only three chromosome pairs showed nucleolar organizer regions, thus indicating that nucleolar competition occurs naturally in hexaploid oats.     

GIEMSA C-BANDED KARYOTYPES OF SEVEN NORTH AMERICAN SPECIES OF ALLIUM

The karyotypes of seven North American Allium species were studied by Giemsa C-banding technique. Two species (A. shoenoprasum and A. tricoccum) were diploids with 2n = 16 chromosomes. Three species (A. cernuum, A. douglasii and A. geyeri) were also diploids but with 2n = 14 chromsomes. Diploid and tetraploid populations of A. textile (2n = 14, 28) were studied. The population of A. canadense studied here was a tetraploid (2n = 28). All these North American species, except A. geyeri, possessed centromeric bands in all their chromosomes and nucleolar constriction bands in their satellited chromosomes. Allium shoenoprasum contained telomeric bands in most of its chromosomes but the other species had them only in a small number of chromsomes. Only three species (A. shoenoprasum, A. textile and A. tricoccum) were found to have intercalary bands in some chromosomes. The heterochromatin distribution in B chromosomes of three species was also observed. In A. cernuum, the heterochromatin occupied most of the length of all its Bs, but in A. shoenoprasum, heterochromatin was concentrated in the centromeric region. One population of A. textile (CC1179) was found to have a B chromosome in which very little heterochromatin existed.     

Systematic relationships within the Microtus arvalis (Rodentia: Cricetidae) group in Iran,inferred from cytogenetic analyses

The distribution of C-heterochromatin and nucleolar organizer regions (NORs) was studied in three species of voles of the Microtus arvalis group in Iran: M. mystacinus, M. kermanensis, and M. transcaspicus. The C-banding pattern and NORs distribution were similar in M. mystacinus and M. kermanensis suggesting taxonomic proximity of these two species. At the same time, the karyotypes of M. mystacinus from Iran were different in C-banding pattern from the complements of conspecific 54-chromosome voles from Europe and other regions of Asia. The most distinct difference was in size of the distal C-positive block of heterochromatin on the X chromosome. In this respect M. mystacinus from Iran and M. kermanensis resembled M. transcaspicus. Small size of the distal C-positive heterochromatic block may be ancestral whereas larger size is derived. The X chromosome of M. transcaspicus can be derived from that of M. mystacinus and M. kermanensis by a large inversion or centromeric shift.     

Computer assisted karyotype analysis of Pyrrhopappus carolinianus

With the help of Computer Aided Karyotyping procedures, Ag-NOR staining and C-banding techniques, the karyotype of Pyrrhopappus carolinianus (Asteraceae, Lactuceae) has been studied. The species has 2n=12 chromosomes. Silver staining reveals that the two shortest pairs of chromosomes possess NOR's. On the basis of chromosome length and centromere position, only the longest chromosome pair and the satellite chromosomes can be identified. Two types of C-banding can be obtained, dependent on the temperature of the hydrochloric acid hydrolysis of the root tips. Hydrolysis at 60°C results exclusively in centromeric bands, whereas a treatment at room temperature reveals a pattern of intercalary bands. A computer assisted analysis of the intercalary banding pattern resulted in the construction of schematic representation of the average C-banding pattern. This banding pattern allows an easy identification of each of the chromosome pairs.     

Karyotypic comparison among Cebuella pygmaea,Callithrix jacchus and C. emiliae (Callitrichidae,Primates) and its taxonomic implications

The karyotype of Cebuella pygmaea (2n=44) obtained by G-, C-banding, and NOR-staining is described. This species presents a heteromorphic C band in the intersticial region of the short arm of chromosome 2. The data obtained were compared with those previously described for the karyotypes of Callithrix jacchus and Callithrix emiliae. The three species differ in the amount and distribution of non-centromeric constitutive heterochromatin. The importance of the variation in constitutive heterochromatin for the phylogeny of the group is discussed. Comparison of the karyotypes in terms of G-banding patterns showed that C. pygmaea and C. emiliae differ from C. jacchus by a Robertsonian translocation and a paracentric inversion, whereas C. pygmaea and C. emiliae differ from each other by a reciprocal translocation between an acrocentric autosome and the short arm of the submetacentric chromosomes that distinguishes their karyotypes from that of C. jacchus. The possible evolutionary paths followed by the karyotypes of the three species are discussed.     

Analysis of the C-banded karyotype of Allium cepa L. Standard system of nomenclature and polymorphism

The C-banded karyotypes of three Allium cepa plants of different background are described. Identification of all chromosomes of Allium cepa is possible on the basis of complex telomeric and intercalary C-bands. A standard system of chromosome nomenclature is proposed. Infraspecific variation in heterochromatin amount per genome, number of intercalary bands per genome, relative area of telomeric bands, relative chromosome length, relative chromosome arm length and centromeric index are statistically analysed. Although extensive polymorphism in Allium cepa chromosomes is found especially with respect to the size of telomeric bands, the overall similarity of the karyotypes is obvious. The value of C-banding for biosystematics of cultivated plants related to Allium cepa and for their breeding is suggested.     

Genome Comparisons with Chromosomal and Molecular Markers for Three Closely Related Flax Species and Their Hybrids

Chromosome C-banding patterns were analyzed in three closely related flax species (Linum usitatissimumL., 2n = 30; L. angustifolium Huds., 2n = 30; and L. bienneMill., 2n = 30) and their hybrids. In each case, the karyotype included metacentrics, submetacentrics, and one or two satellite chromosomes. Chromosomes of the three flax species were similar in morphology, size (1–3 m), and C-banding pattern and slightly differed in size of heterochromatic regions. In all accessions, a large major site of ribosomal genes was revealed by hybridization in the pericentric region of a large metacentric. A minor 45S rDNA site was observed on a small chromosome in L. usitatissimum and L. bienne and on a medium-sized chromosome in L. angustifolium. Upon silver staining, a nucleolus-organizing region (NOR) was detected on a large chromosome in all species. InL. angustifolium, an Ag-NOR band was sometimes seen on a medium-sized chromosome. In the karyotypes of interspecific hybrids, silver-stained rDNA loci were observed on satellite chromosomes of both parental species. RAPD analysis with 22 primers revealed a high similarity of the three species. The greatest difference was observed between L. angustifolium and the other two species. The RAPD patterns of L. bienne and L. usitatissimum differed in fewer fragments. A dendrogram of genetic similarity was constructed for the three flax species on the basis of their RAPD patterns. Genome analysis with chromosome and molecular markers showed thatL. bienne must be considered as a subspecies of L. usitatissimum rather than a separate species. The three species were assumed to originate from a common ancestor, L. angustifoliumbeing closest to it.     

Chromosomal differentiation in two species of Aedes and their hybrids revealed by giemsa C-banding

Giemsa C-banding patterns in two species of mosquitoes, Aedes aegypti and Aedes mascarensis, their hybrids and backcross progeny revealed differences in the sex chromosome pair. In A. aegypti, the female determining or the m chromosome in both males and females shows a conspicuous band in the centromere region and another band in one arm. The male determining or the M chromosome is devoid of any bands. Progeny of crosses involving A. aegypti females and A. mascarensis males showed interesting albeit unexpected results. The intercalary band was suppressed in both sons and daughters. When such F₁ sons were backcrossed to A. aegypti females, a proportion of males developed into intersexes. These intersex progeny differed from the normal males in terms of their banding pattern. In the reciprocal cross (A. mascarensis female × A. aegypti male), the F₁ and the backcross progeny yielded the expected C-banding patterns. The implications of the reversible expression of the intercalary band on the A. aegypti m chromosome and its relevance to genetic regulation are discussed.     

Chromosome plasticity in Ctenomys (Rodentia Octodontidae): chromosome 1 evolution and heterochromatin variation

A chromosome 1 (Cr1) pericentric inversion is described in six of seven species in the genus Ctenomys (tuco-tucos) from Uruguay. The inversion was inferred from G-band analyses of subtelocentric Cr1 hypothesised to be derived from the ancestral metacentric condition. Cr1 varies across species in heterochromatin amount and localisation including a metacentric chromosome without positive C-bands in C. torquatus, a subtelocentric chromosome with heterochromatic short arms in C. rionegrensis, and a subtelocentric chromosome negative after C-banding in five of the species analysed here. Pachytene chromosomes from C. rionegrensis, a species with the highest heterochromatin content, and C. torquatus, one of the species with the lowest heterochromatin content, were analysed in order to assess possible mechanisms of heterochromatin evolution. This analysis revealed the presence of three heterochromatic chromocenters in C. rionegrensis where bivalents converge, while in C. torquatus only one chromocenter was observed. In both species, highly repetitive DNA was observed, localised in chromocenters after “in situ” hybridisation. Heterochromatin associated protein M31 was localised in chromocenters of both species after immuno-detection. The spread of heterochromatin in Ctenomys chromosomes could be produced by chromatin exchanges at the chromocenter level. We propose the exchange of this DNA associated proteins between non-homologous chromosomes in pachytene to be the responsible for the spread of heterochromatin through the karyotypes of species like C. rionegrensis     

Characterization of different types of condensed chromatin inCostus (Zingiberaceae)

The chromatin structure of six diploids species ofCostus was analysed using conventional Giemsa staining, C-banding and DAPI/CMA fluorochromes. The interphase nuclei in all the species show an areticulate structure and the prophase chromosomes show large blocks of proximal condensed chromatin. After banding procedures, each chromosome exhibits only centromeric dot-like DAPI⁺/CMA^– C-bands whereas the satellites (one pair at each karyotype) are weakly stained after C-banding and show a DAPI^–/CMA⁺ fluorescence. Two chromocentres show bright fluorescence with CMA and weak staining after C-banding whereas the others chromocentres show only a small fraction of DAPI⁺ heterochromatin. These results were interpreted to mean that the greater part of the condensed chromatin has an euchromatic nature whereas two types of well localized heterochromatin occur in a small proportion. The Z-stage analysis suggests that heterochromatin and condensed euchromatin decondense at different times. The chromosome number and morphology of all species are given and the implications of the condensed euchromatin are discussed.Dedicated to Prof.Elisabeth Tschermak-Woess on the occasion of her 70th birthday.     

Chromosome bands in freshwater triclads

Four species of Triclads belonging to three families, Dugesia polychroa and Dugesia mediterranea (Dugesiidae), Planaria torva (Planariidae) and Dendrocoelum lacteum (Dendrocoelidae) were studied for chromosome banding: C-banding for all the species, ASG banding for Dugesia polychroa and G-banding for Dugesia polychroa and Dugesia mediterranea. C-banding results for Dugesia lugubris-polychroa group suggest a high level of heterochromatin evolution in the group. Small bands strictly limited to the centromeric region were seen in Dugusia lugubris and this pattern is similar to the patterns of some species belonging to other families, notably Planaria torva and Dendrocoelum lacteum. This could be considered a primitive character. In contrast numerous heterochromatin bands which are useful to characterize the different karyotypes were seen in Dugesia polychroa and Dugesia mediterranea. Our data suggest that heterochromatin is important in freshwater triclad speciation.     

The late replication banding patterns of chromosomes are highly conserved in the genera Rana,Hyla, and Bufo (Amphibia: Anura)

Late replication banding and C-banding analyses were performed on the metaphase chromosomes of six species and one subspecies of Palearctic water frogs, genus Rana. Although C-banding patterns showed interspecific or intersubspecific variation, late replication banding patterns of all 13 chromosome pairs of these species were homologous. Minor differences of banding patterns were observed only in chromosomes 2, 7 and 13. Close comparison of the late replication banding patterns with those of three non-water frog species of Rana, and one each of Hyla and Bufo, provided important information on interspecific and intergeneric variability. In the Rana species, the banding patterns of all 13 pairs were homologous except for those some regions of 8 pairs. In one species each of Hyla and Bufo that was examined, the six large chromosome pairs (Nos. 1-6) showed banding homologies. Furthermore, among the Rana, Hyla and Bufo species the four large chromosome pairs (Nos. 1-3, 5 of Rana and Hyla, and Nos. 1, 3–5 of Bufo) shared banding homologies. These results show that the large chromosomes have been highly conserved in the evolutionary history of the three genera.     

Cytogenetic Analysis of Diploid <Emphasis Type="Italic">Avena</Emphasis> L. Species Containing the As Genome

Cytogenetic examination showed that three diploid oat species containing the As genome are highly similar in karyotype structure and chromosome C-banding patterns. Avena strigosa is more similar to A. wiestii, while A. hirtula is to an extent separated from the two species, differing in the C-banding pattern of chromosome 6. The karyotypes of all three species harbor a small acrocentric chromosome, which is absent from diploid oat species containing other variants of the A genome. The results made it possible to assume genome specificity of the rearrangement resulting in this chromosome.     

Comparative cytogenetic analysis of hexaploid <Emphasis Type="Italic">Avena</Emphasis> L. species

Using C-banding method and in situ hybridizatiion with the 45S and 5S rRNA gene probes, six hexaploid species of the genus Avena L. with the ACD genome constitution were studied to reveal evolutionary karyotypic changes. Similarity in the C-banding patterns of chromosomal patterns and in the patterns of distribution of the rRNA gene families suggests a common origin of all hexaploid species. Avena fatua is characterized by the broadest intraspecific variation of the karyotype; this species displays chromosomal variants typical of other hexaploid species of Avena. For instance, a translocation with the involvement of chromosome 5C marking A. occidentalis was discovered in many A. fatua accessions, whereas in other representatives of this species this chromosome is highly similar to the chromosome of A. sterilis. Only A. fatua and A. sativa show slight changes in the morphology and in the C-banding pattern of patterns of chromosome 2C. These results can be explained either by a hybrid origin of A. fatua or by the fact that this species is an intermediate evolutionary form of hexaploid oats. The 7C–17 translocation was identified in all studied accessions of wild and weedy species (A. sterilis, A. fatua, A. ludoviciana, and A. occidentalis) and in most A. sativa cultivars, but it was absent in A. byzantina and in two accessions of A. sativa. The origin and evolution of the Avena hexaploid species are discussed in context of the results.     

A comparative analysis of the karyotypes of Cricetus cricetus and Cricetulus griseus

This study presents a comparison of the mitotic chromosomes of the two species of hamsters Cricetus cricetus (European hamster) and Cricetulus griseus (Chinese hamster), which have the same chromosome number of 2n=22. — G-banding procedure reveals striking similarities in both karyotypes and gives the possibility to analyse structural changes so that two examples for Robertsonian rearrangement can be observed. — A remarkable kind of difference between the two karyotypes becomes obvious after C-banding procedure. While Cricetus cricetus shows a large amount of predominantly centromeric heterochromatin, in Cricetulus griseus C-bands are less conspicuous, and a few chromosomes do not exhibit any centromeric heterochromatin at all.     

HETEROCHROMATIN BANDING IN BOYKINIA,HEUCHERA, MITELLA,SULLIVANTIA, TIARELLA,AND TOLMIEA (SAXIFRAGACEAE)

Karyotypic differences were sought among species of Boykinia, Heuchera, Mitella, Sullivantia, Tiarella, and Tolmiea utilizing a modification of the Hy-banding technique. Prominent centromeric and some telomeric heterochromatin banding was observed. Boykinia aconitifolia and species of Sullivantia possess an identical banded karyotype, while four species of Heuchera, Mitella diphylla, Tiarella cordifolia, and Tolmiea menziesii (the latter at the tetraploid level) are characterized by a second, slightly different banded karyotype. In Sullivantia, Giemsa C-banding stains the same chromosomal regions revealed by Hy-banding. Larger amounts of heterochromatin are present in chromosomes of species of Heuchera, Mitella, Tiarella, and Tolmiea than in chromosomes of Sullivantia species and Boykinia aconitifolia. These karyological observations confirm generic relationships and demonstrate the systematic applicability of chromosome banding techniques to plants with very small chromosomes.     

Cytological characterization of heterochromatin and rDNA inPinus radiata andP. taeda

Fluorochrome C-banding ofPinus radiata andP. taeda metaphase chromosomes showed many pericentromeric DAPI bands and interstitial CMA bands inP. radiata, and centromeric and interstitial CMA bands inP. taeda. Giemsa C-band patterns differed between the species with centromeric bands inP. radiata but no consistent bands inP. taeda. A karyotype ofP. radiata was developed based on banding patterns that distinguished all but two of the 12 pairs of chromosomes. In situ hybridization (ISH) using probes for high-copy ribosomal DNA (rDNA) showed 10 pairs of 18S–25S sites and two pairs of 5S sites in both species. Most of the sites were interstitial or centromeric.     

DNA composition in South American camelids I. Characterization and in situ hybridization of satellite DNA fractions

The DNA composition and the in situ hybridization of satellite fractions were analysed in the New World camelids llama, alpaca, guanaco and vicuña. In the four camelid forms, it was possible to identify a similar main band DNA and five satellite fractions (I–V) with G+C base contents ranging from 32% to 66%. Satellites II–V from llama were in situ reannealed on chromosomes from the four camelid forms. The results obtained were: (a) the four satellites hybridized with regions of C-banding (centromeric regions of all chromosomes and short arms of some autosomes); (b) in general, homologous hybridizations (llama DNA versus llama chromosomes) were more efficient than heterologous reassociations; there were however three exceptions to this rule (vicuña and alpaca satellite fraction II, chromosome group B; vicuña fraction V, chromosome groups A and B); (c) X chromosomes from the four camelids had satellites III–V but lacked satellite II, (d) no satellite fraction was detected on chromosome Y. The analysis of the in situ hybridization patterns allowed to conclude that most or all C-banded chromosome regions comprise several satellite DNA fractions. It is, moreover, proposed that there is an ample interspecies variation in the number of chromosomes that cross-react with a given satellite fraction. Our data give further support to the close genomic kinship of New World camelids.     

Cytogenetic analysis of Ctenostomini by C-banding and rDNA localization and its relevance to the knowledge of the evolution of tiger beetles (Coleoptera: Cicindelidae)

In this work, the first cytogenetic data on Neotropical Collyrinae is provided, by way of their karyotypes, C-banding and ribosomal genes (rDNA) localization using fluorescence in situ hybridization (FISH). The two species analysed, Ctenostoma (Procephalus) ornatum ornatum (male) and Ctenostoma (Euctenostoma) rugosum(female) showed, respectively, a diploid number of 17 and 18 chromosomes. C. ornatum ornatum has a multiple sex chromosome system ( n=7 + X₁X₂Y), and mitotic and meiotic metaphase cells showed rDNA gene labelling in the smallest autosomal pair. In this species, no C-bands were obtained, while C. rugosum seems to exhibit centromeric and/or interstitial C-bands in almost all chromosomes. The observation of a multiple sex chromosome system in Ctenostomini ensured the appearance of this characteristic in the hypothetical ancestral of Collyrinae and Cicindelini. The subfamily Collyrinae is not uniform in what concerns diploid chromosome number and rDNA gene localization, because C. ornatum ornatum possesses a lower chromosome number and autosomal rDNA genes when compared with the other Collyrinae species studied ( Neocollyris spp.). Independent events leading to the reduction in chromosome number might have taken place during the split of the Collyrinae into the tribes Ctenostomini and Collyrini.