Heterochromatin Bands Research Articles

Karyomorphological analyses and heterochromatin characteristics disclose phyletic relationships among 2n = 32 and 2n = 36 species ofOrchis (Orchidaceae)

The karyotypes of eight taxa ofOrchis L. with 2n = 32 and 2n = 36 have been investigated using morphometrical measurements following staining with Feulgen, Giemsa (C-banding) and the DNA specific fluorochrome Hoechst 33258. The karyotypes ofO. coriophora subsp.fragrans, andO. papilionacea proved to be the most asymmetrical, whileO. morio andO. longicornu exhibited the most symmetrical karyotypes. Using C-banding and the fluorochrome H33258 only the taxa with high asymmetry indices showed the presence of differentially stained chromatin bands. In most chromosomes heterochromatin bands were present at the telomeric position. The present results seem to indicate that the analysed species do not form a homogeneous group and further subdivisions are possible, which, in turn, do not always correlate with divisions based on morphological characters. Both karyomorphology and heterochromatin distribution coincide in indicating a possible evolutionary pathway.

Karyomorphological and heterochromatin similarities among fourVigna species

Karyomorphological similarities among four species of the genusVigna, V. unguiculata, V. luteola, V. oblongifolia andV. vexillata, were evaluated. Two different approaches were followed: cytomorphometrical determinations, carried out with an automated image analysis system to improve resolution, yielded some karyotypical indices; the distribution of heterochromatin bands was interpreted using a recently reported algorithm.

Cytosystematics of Five North American Amblyomma (Acarina: Ixodidae) Species

The karyotypes of 5 species of Amblyomma ticks found in North America were examined for the presence and location of constitutive heterochromatin (C-bands). All specimens examined had 20 autosomes and an XX:XO sex-determining system, with the X being the largest element in the karyotype. Except as noted in text, the autosomes of all species were acrocentric and heterochromatin was restricted to the centromeric region. The third largest autosome in 4 of the 5 species displayed a consistent band of heterochromatin just below the centromere; Amblyomma imitator displayed heterochromatin on the third largest pair of autosomes but in the form of an entire heterochromatic short arm. It is hypothesized that the third largest autosome could be the location of the nucleolar organizer region. Unique features of the C-banded karyotype that characterize and differentiate each species are presented. Similarity in the C-banding pattern exists between Amblyomma americanum and Amblyomma maculatum (the C-band in the X chromosome) and Amblyomma cajennense and A. imitator (the extreme subacrocentric X chromosome). The placement of Amblyomma inornatum remains difficult and cannot be clearly determined based on the placement of heterochromatin.

Karotypic characterization of turbot (Scophthalmus maximus) with conventional, fluorochrome and restriction endonuclease-banding techniques

A karyotypic analysis was carried out in turbot (Scophthalmus maximus) using conventional banding techniques, fluorochromes and restriction endonucleasebanding. The standard karyotype of turbot is 2n=44 chromosomes, with 48 chromosome arms. Nucleolar organizer regions, which were localized in the short arm of Chromosome Pair No. 3, showed C-and chromomycin A3-positive staining. C-bands were mainly located at the centromeres, but were also present in some interstitial and telomeric locations. No differences were revealed among constitutive heterochromatin bands after treatment of fixed chromosomes with fluorochrome staining and restriction endonucleases. Digestion with DdeI restriction enzyme produced a pattern of interstitial banding which suggested some degree of differentiation along the chromosome arms in turbot. Neither variation in chromosome number of arm number nor polymorphism in nucleolar organizer regions was revealed in the turbot analyzed.

A new heterochromatin banding pattern revealed by modified HKG banding technique in maize chromosomes

A new heterochromatin banding pattern revealed by modified HKG banding technique in maize chromosomes

N‐ and C‐banded Karyotypes of Two Parasorghum Species, Sorghum Purpureo‐Sericeum and S. versicolor

Chromosome banding patterns, showing number, location, and size of heterochromatin bands, provide unique ways to identify individual chromosomes of a complement and to elucidate phylogenetic relationships among related species. However, no report is available describing banding characteristics of chromosomes for the 10‐chromosome Parasorghum spp. Therefore, the objectives of this research were to develop banding techniques suitable for the sorghum chromosomes and to depict their banding patterns. Heterochromatin banding methods (N‐ and C‐banding) were applied and the N‐ and C‐banded karyotypes were depicted for two Parasorghum species, Sorghum purpureo‐sericeum Aschers & Schweinf and S. versicolor Anderss. All chromosomes of S. purpureo‐sericeum had intensive centromeric N‐ and C‐hands on both arms, except chromosome 4, which showed a faint centromere N‐band on the long arm. Chromosomes 1, 3, and 4 showed prominent telomeric N‐ and C‐hands on short arms, in addition to the intensive intercalary N‐bands, whereas chromosomes 2 and 5 had only intensive intercalary N‐ and C‐bands on short arms. Chromosomes 3 and 4 showed faint telomeric N‐bands and intensive telomeric C‐bands on the long arm. For S. versicolor, chromosomes 1, 3, 4, and 5 showed intensive centromeric N‐ and C‐bands. Telomeric N‐ and C‐bands were faint on the long arms of chromosomes 1 and 4 and were not found on long arms of chromosomes 2, 3, and 5. Chromosome 2 had faint intercalary N‐ and C‐bands on the long arm and also a faint centromeric C‐band. For chromosomes 1, 2, and 5, N‐ and C‐banded karyotypes of the two Parasorghum species were similar, but not identical. Some variation existed between N‐ and C‐banding patterns for the same species. The N‐ and C‐banding patterns for chromosomes in S. purpureo‐sericeum and S. versicolor should be useful in identifying individual chromosomes, in detecting structural aberrations, and in evaluating their phylogenetic relationships with other Sorghum species.

Cytogenetic study of F1 hybrids betweenCrepis dinarica andCrepis froelichiana (Asteraceae)

Crepis dinarica andC. froelichiana are two closely related species of theC. praemorsa complex. Even though they exhibit the same chromosome number (2n = 8) and similar idiogram shape, they differ widely in quantity and distribution of heterochromatin bands. The hybrids between these two species comprise three morphological types. Parental genomes were distinguished in hybrids by Giemsa differential staining (C-banding). Although meiosis presents only a few abnormalities (about 2.4%), the percentage of aborted pollen grains is very high (90%).

Genetic mapping between Gli-B1 locus and a telomeric C-heterochromatin band in wheat

Using C-banding it has been possible to prove that the bread wheat varieties 'Holdfast' and 'CapelleDesprez' shows an intense band of telomeric heterochromatin on the short arm of chromosome 1B, while the variety 'Pané-247' presents a very thin band. Gliadin study using pH-acid electrophoresis revealed the existence of differences in the Gli-B1 locus in the three varieties. Analysis of the progeny of the (P x H) x CD hybrid revealed recombination between the heterochromatin C-band and locus Gli-B1, and allowed the genetic distance between the two markers to be calculated as 6.55±3.16 cMorgan. This is the first time the genetic distance from a locus to the chromosome telomere has been directly obtained in wheat. The heterochromatin C-band studied here gives us a cytological marker on chromosome 1B that can be used as a reference point in the localization of other genes.

Macrophage-like cells in the presumptive optic pathways in the floor of the diencephalon of the chick embryo

In the suboptic necrotic centres (SONCs) of the chick embryo diencephalon floor, large numbers of cells die in Hamburger and Hamilton's (HH) developmental stages 14-23. Until recently, it was thought that in these centres, the fragments of dead cells were phagocytosed exclusively by neighboring healthy cells but not by specialized macrophages. We now report morphological evidence of macrophage-like cells within the SONCs of the chick embryo. The distinctive features of these cells are their more or less spherical shape, a nucleus with a thin band of heterochromatin just beneath the nuclear envelope, and cytoplasm showing abundant digestive vacuoles and mitochondria with an electron-lucent matrix. These cells are capable of undergoing mitosis, and selectively stain with the histochemical technique for acid phosphatase. The macrophage-like cells are rare in SONCs in stages HH14-20 and become much more abundant in developmental stages just before the disappearance of these necrotic centres, suggesting that they phagocytose debris from the last cells to die in the SONCs. Acid phosphatase-positive mesenchymal cells with morphological features similar to those of macrophage-like cells are seen in intimate relationship with the basal surface of the SONCs in places where the basal lamina is sometimes missing. These observations suggest that macrophage-like cells in the SONCs arise from the underlying mesenchyme. Free macrophage-like cells with mitotic capacity are also seen in the ventricular lumen adjacent to the apical surface of the diencephalon floor in zones related to the presumptive optic pathways. These cells phagocytose cell debris shed from both the SONCs and from the partially disorganized areas in the neuroepithelium. In these latter we have identified mesenchymal cells with morphological features similar to the macrophage-like cells in the process of traversing the neuroepithelium from the mesenchymal compartment toward the ventricular lumen, thus suggesting that the intraventricular macrophage-like cells arise from the mesenchyme underlying the diencephalon floor.

Cytosystematics of Five North American Dermacentor (Acari: Ixodidae) Species

The karyotypes of five species of Dermacentor ticks found in North America were examined for the presence and location of constitutive heterochromatin (C-bands) and the location of the nucleolar organizing regions (NORs). All specimens examined had 20 autosomes and an XX:XO sex-determining system; the X was the largest element in the karyotype. Except as noted, the autosomes of all species were acrocentric, and heterochromatin was restricted to the centromeric region. The one-host species D. nitens and D. albipictus were distinguished from the three-host species by a lack of additional bands of heterochromatin and by having a subtelocentric X chromosome. However, some individuals of D. albipictus were observed to have acrocentric X chromosomes. D. nitens differed from D. albipictus in having two subtelocentric autosomal pairs (pairs 1 and 8). A single pair of NORs was noted for the one-host species; however, heterochromatin was not associated with the NORs. Among the three-host species, D. occidentalis showed a band of heterochromatin proximal to the centromere in autosomal pairs 1 and 8, and D. andersoni had similar bands in autosomal pairs 1, 3, 7, and 9. D. variabilis displayed heterochromatic bands in autosomal pairs 3, 7, and 9. All three-host species displayed a single pair of NORs, which was associated with the band of heterochromatin on pair 9. Indications of some genetic incompatibility between the two recognized forms of D. albipictus are discussed.

New Focus for Engineering Support at the Central Experimental Farm

The significance of the 4C value (where C is the amount of DNA in the unreplicated haploid genome) in angiosperm plants is discussed. The DNA amount is a stable feature used in biosystematics. Although this parameter varies even in closely related taxa, there is no correlation between the DNA amount and the structural and functional organization of plants. The role of DNA amount, including “excess” DNA, in plant evolution is considered. Some rules governing the distribution of DNA amount among different plant taxa are postulated, together with the possibility of using the data in systematics, phylogeny, and solutions of problems of genetic apparatus organization and evolution. The decrease in DNA value per genome during plant evolution and the high level of species formation in taxa with large DNA values have been shown. Plant taxa with a small DNA value per genome have a high percentage and higher degree of polyploidy. The nature of the differential staining of euchromatin and heterochromatin bands of prophase and metaphase chromosomes is also discussed. Data that could explain the mechanism of heterochromatin visualization under cold pretreatment of cells are reviewed. Phenomena involved in the arrangement of chromocenters in interphase nuclei and chromosomes in metaphase during consecutive cell generations are discussed.

Genome analysis in higher plants

Gordon Kimber introduced the workshop topics that were designed to illustrate several facets of genome analysis in higher plants. Kimber's presentation covered genome analysis by chromosome pairing in hybrids. He emphasized that this is the only method in which at least some DNA is sampled along the entire length of the chromosomes. Moreover, originally based on total pairing, genome analysis has now been extended to include numerical assessments of the patterns of pairing. Genome analysis is most accurate in those hybrids where there is pairing competition; for example in diploid x allopolyploid hybrids. There are various models of pairing at increasing levels of ploidy that can be used to calculate relative measures of affinity among the genomes. In the ensuing discussion,, Kimber pointed out that genes affecting chromosome pairing do not alter the results of genome analysis as they influence overall pairing, but not the pattern of pairing. Limitations to genome analysis were also discussed. For example, chromosome pairing in diploid hybrids cannot be considered a reliable indication of relationship because of lack of competition for synaptic partners. Similarly, plants with small chromosomes are also unsuitable for genome analysis as differences between rod and ring bivalents cannot be distinguished. Second speaker, B. S. Gill, spoke on the use of heterochromatin banding and in situ hybridization in assaying subgenomic affinities. These techniques provide additional and complementary information to genome analysis by chromosome pairing. The subgenomic affinities that can be assayed include individual chromosome and chromosome arm homologies and specific DNA sequence homologies. Individual chromosome homologies have been assessed by banding analysis of metaphase I configurations in meiocytes. Somatic chromosome banding analysis provides additional information on the amount, location, and structure of heterochromatin. In situ hybridization has been used to study the amount and location of specific DNA sequences in different genomes. Such marked chromosomes can be traced in natural and experimental introgressive hybridization studies. Southern blotting analysis with defined DNA sequences (rDNA, as an example) at different 'stringencies of hybridization can be used to discern evolutionary relationship among taxa. The questions involved strategies for cloning of DNA sequences for molecular cytogenetics analysis. The third speaker, K. Tsunewaki described the role of plasmon analysis as a means of identifying cytoplasm donor to polyploid species. Cytoplasm of various Aegilops species have been substituted with the nucleus of Triticum aestivum. From the phenotypes of such alloplasmic lines, it has been possible to trace diploid donor of cytoplasm of polyploid Triticum and Aegilops species. More recently, restriction digestion analysis of chloroplast and mitochondrial DNA has been used for assaying cytoplasmic affinities. Some of the problems with the use of plasmon analysis in phylogenetic affinities were discussed. First of all, there is intraspecific variation in both mitochondrial and chloroplast DNAs. Another potential problem is the male transmission of cytoplasmic organelles, although in wheat no such male transmission has been documented. The final speaker, D. F. Weber, discussed the use of restriction fragment length polymorphisms (RFLPs) in corn improvement. He elaborated on the methodology and applications of RFLP analysis. In addition to their use as molecular markers, RFLPs are also useful in uncovering single gene or small chromosomal duplications or other aberrations that cannot be detected by pairing analysis. About 400 RFLP loci have been mapped in corn. About 20 % of the loci were found to be duplicated either on the same chromosome or were dispersed on many chromosomes. The A-B translocations were useful in chromosome arm assignment of RFLP loci, in mapping of centromeres, and in aligning RFLP linkage maps with chromosome maps and conventional linkage maps. There was considerable discussion on the advancement of RFLP maps in different taxa. It was suggested that there should be a coordination of the work on RFLP maps and on comparative gene mapping. Annual meetings of the Genetics Society of Canada or America could provide forums for joint meetings of RFLP workers in plants. The workshop ended on a note of thanks by Kimber to participating speakers and the audience. About 60 people participated and the workshop was considered a success.

Chromosome differentiation in the Triturus alpestris complex (Amphibia: Caudata)

Several individuals from distinct populations of 7 subspecies included in the Triturus alpestris complex have been analysed to obtain characteristic C-banding patterns. The differences found among the populations as regards the amount, complexity and distribution of heterochromatin bands have been employed to test a pattern of chromosome evolution. Relevant similarities and dissimilarities of these populations are discussed in the light of the tentative evolutionary history inferred from a rooted tree.

Giemsa C-banded karyotypes of Avena species

Giemsa C-banding was used to identify individual somatic chromosomes in eight diploid species of Avena. Two patterns of heterochromatin distribution were found. The chromosomes of five A genome species (A. strigosa, A. hirtula, A. longiglumis, A. damascena, and A. canariensis) possessed mainly telomeric bands, whereas those from three C genome species (A. clauda, A. pilosa, and A. ventricosa) were characterized by higher chromatin condensation and several intercalary heterochromatin bands. The divergent evolution between the two groups is confirmed after C-banding. The unique C-banding patterns of several chromosomes in each species will be a useful tool for the study of meiotic behaviour in interspecific hybrids among Avena spp.Key words: C-banding, Avena, heterochromatin.

Heterochromatin banding in the genus Paris

The heterochromatin content of new accessions of the genus Paris have been studied using ‘C’ banding and ‘Q’ banding techniques. Supernumerary chromosomes in two accessions are shown to differ in their heterochromatin content. The results are related to previous cytogenetic work in the genus Paris.

C‐BANDING KARYOTYPE AND MALE MEIOSIS OF ACROPHYLLA WUELFINGI (REDTENBACHER) (PHASMATODEA: PHASMATIDAE)

AbstractThe C‐Banded karyotype and the male meiosis of the Australian species Acrophylla wuelfingi are described and compared with other members of the subfamily Phasmatinae. The chromosomes of A. wuelfingi are rather large and their number is 2n ♂= 45, XO, 2n ♀= 46, XX; the metacentric X being the largest element of the set. Karyotype analysis shows a predominance of heterobrachial chromosomes and centromeric heterochromatin bands or blocks in all elements. Male meiosis is chiasmate, with mainly terminal chiasmata.

Translocations and other karyotypic structural changes in wheat x rye hybrids regenerated from tissue culture

The spontaneous occurrence of chromosome breaks, deletions, and translocations in plant tissue cultures is well documented. This study investigated the usefulness of tissue culture as a method of introgressing alien genes into wheat. Wheat X rye hybrids were regenerated from embryo scutellar calli maintained in culture for 222 days. The regenerated seedlings then were treated with colchicine to produce amphidiploids (AABBDDRR). The karyotypes of ten amphidiploids were analyzed by C-banding to determine chromosome structural changes that occurred during tissue culture. Three wheat/rye and one wheat/wheat chromosome translocations, seven deletions, and five amplifications of heterochromatin bands of rye chromosomes were identified. One amphidiploid contained a reciprocal translocation between wheat chromosome 4D and rye chromosome 1R. Non-reciprocal translocations between 2B and 3R, and between an unidentified wheat chromosome and 2R, were found independently in two amphidiploids. An additional plant had a translocation between wheat chromosomes 6B and 5A. All deletions involving rye chromosomes were noted in all 10 amphidiploids. Twelve of the 13 breakpoints in chromosomes involved in translocations and deletions occurred in heterochromatin. Amplification of heterochromatin bands on 2RL and 7RL chromosome arms also was observed in five plants. These results indicate a high degree of chromosome structural change induced by tissue culture. Therefore, tissue culture may be a useful tool in alien gene introgression and manipulation of heterochromatin in triticale improvement.

Identification of C-banded chromosomes in meiosis of common wheat, Triticum aestivum L.

The C-banding pattern of nine meiotic chromosomes of common wheat (Triticum aestivum L.) as described. In F1s of crosses between monosomics of 'Chinese Spring' and two Spanish wheat cultivars, univalent chromosomes were used to aid the recognition and analysis of the C-banding pattern for the individual chromosomes. The identification of one chromosome involved in one translocation in 'Chinese Spring' x 'Pané 247' has been made through heterochromatin bands observed in the chromosomes involved in multivalents.

Cytogenetics of the chinese giant salamander, Andrias davidianus (Blanchard): the evolutionary significance of cryptobranchoid karyotypes

Cytogenetic aspects of the cryptobranchid salamander Andrias davidianus of western China have been studied, including chromosome number and morphology, C-band patterns, meiosis, and the chromosomal localization of ribosomal 5S RNA genes. Our data regarding chromosome number (2n=60) and general chromosome morphology largely confirm the results of Morescalchi et al. (1977). The karyotype consists of 16 pairs of “macrochromosomes” that decrease gradually in relative length to 14 pairs of “microchromosomes”. Telocentric chromosomes are a conspicuous feature of the karyotype, representing more than half the genome. Differential staining reveals that all of the chromosomes, except four pairs of microchromosomes, have C-band heterochromatin in their centromeric regions, the amount varying irrespective of chromosome size. Faint bands of interstitial and telomeric C-band heterochromatin are found in mitotic chromosomes but are not seen in meiotic preparations. In C-banded mitotic preparations from a female, one of the smallest macrochromosome pairs is heteromorphic in respect to C-band heterochromatin and centromere position. In situ hybridization of an iodinated 5S RNA probe to meiotic chromosome preparations reveals that this repeated gene is clustered near the telomeric region of chromosome 7, a medium size telocentric, a location corresponding to a band of heterochromatin. Studies of spermatocytes indicate that the process of meiosis in A. davidianus closely resembles that of more advanced salamanders, and that the microchromosomes are meiotically stable. The significance of microchromosomes and chromosome morphology in the reorganization of salamander genomes during evolution is discussed on the basis of cytogenetic data available for A. davidianus and various other primitive and advanced salamanders.

C-banding pattern and meiotic pairing in five rye chromosomes of hexaploid triticale

The meiotic behaviour of rye chromosomes 1R, 2R, 3R, 6R and 7R/4R of hexaploid triticale 'Cachirulo' is analyzed using the C-banding technique. These chromosomes show different C-banding patterns and present different pairing levels at metaphase I. A decreasing effect of large telomeric heterochromatin bands on pairing is deduced from the following two main facts: i) The chromosome 7R/4R shows the highest pairing associated with the smallest amount of heterochromatin, ii) pairing levels of 2 R short arm and 3 R long arm which carry large telomeric bands are less than their respective long and short arms lacking telomeric heterochromatin. Possible desynaptic effects of heterochromatin are discussed although an asynaptic effect cannot be rejected.