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  • 1
    Electronic Resource
    Electronic Resource
    Heterochromatin accumulation, disposition and diversity in Gibasis karwinskyana (Commelinaceae) (1991)
    Springer
    Chromosoma 100 (1991), S. 467-478 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract C-banding differences within Gibasis karwinskyana (Roem & Schult.) Rohw. were reassessed using dual fluorochrome staining. Pronounced differences in C-band pattern between two subspecies with identical basic karyotypes were due to different chromosomal locations of AT-rich and GC-rich heterochromatin. The AT-rich component had an equilocal distribution in the karyotype and has evidently been accumulated at telomeres, as shown by its prevalence in supernumerary segments and B chromosomes. The GC-rich component also varied in amount, but was limited to nucleolus organizing regions (NORs) and centromeres. Centromeres and telomeres are suggested to constitute separate, although perhaps interdependent, centres of heterochromatin amplification. The possible role of nuclear architecture in determining the accumulation, distribution and spread of these sequences is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00364557
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  • 2
    Electronic Resource
    Electronic Resource
    Autosyndetic pairing in Gibasis (Commelinaceae) hybrids revealed by C-banding (1985)
    Springer
    Chromosoma 92 (1985), S. 176-184 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Two closely related species of Gibasis, G. karwinskyana and G. consobrina, and their F1 hybrids were studied cytologically at the diploid and tetraploid level. Despite similarity in their basic karyotype, pairing was extremely limited in the diploid hybrid and almost exclusively autosyndetic in the tetraploid, except for multivalent formation due to interchange heterozygosity. The analysis was considerably facilitated by the use of C-banding techniques at meiosis, by which the chromosomes of each species could be readily identified. In the parents, quadrivalents were formed between homologous but non-identical chromosomes, which also formed autosyndetic bivalents in the hybrids. Meiotic pairing in the hybrids was unaffected by polytypy for C-bands among different populations of the parental species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00348691
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  • 3
    Electronic Resource
    Electronic Resource
    Genomic in situ hybridization reveals the allopolyploid nature ofMilium montianum (Gramineae) (1992)
    Springer
    Chromosoma 101 (1992), S. 420-424 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Molecular techniques that “paint” chromosomes offer exciting new opportunities for testing genome relationships.Milium montianum (2n=22) is a grass whose distinctive bimodal karyotype comprises 8 large (L-) and 14 smaller (S-) chromosomes. The proposal thatM. montianum is an allotetraploid, with diploidMilium vernale (2n=8) as the L-chromosome genome donor, has been impossible to confirm by classical means. To test this hypothesis, biotinylated total genomic DNA of diploidM. vernale (2n=8) was hybridized in situ to root tip chromosomes ofM. montianum. TheM. vernale probe hybridized preferentially to all L-chromosomes, but not to the S-chromosomes. These results (i) confirm the allopolyploid nature ofM. montianum, (ii) strongly support the theory that the L-chromosomes ofM. montianum were donated byM. vernale, or a closely related genotype and (iii) show that subsequently the L-chromosomes have largely retained their genomic integrity in the new allopolyploid backgroud. Clearly, genomic in situ hybridization (GISH) is a potentially powerful tool for studying genome evolution and biosystematics. It will often be useful for investigating the origins of wild and cultivated polyploid plant species, especially where conventional methods have failed, for studying introgression, and for understanding the mechanism(s) of origin of bimodal karyotypes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00582836
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  • 4
    Electronic Resource
    Electronic Resource
    Identification of Renner complexes and duplications in permanent hybrids of Gibasis pulchella (Commelinaceae) (1987)
    Springer
    Chromosoma 95 (1987), S. 424-434 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Discovery of permanent hybridity in the very large chromosomes of Gibasis pulchella (Commelinaceae) has allowed specific identification of segmental interchanges in complex heterozygotes. The interchanges are confined to terminal regions, are sometimes very small, and may be unequal in size. Breakpoints have occurred close to major C-bands, probably at euchromatin/heterochromatin boundaries. Complete and disjunctional ring formation at meiosis results in the segregation of two Renner complexes, each of which can be specifically identified with C-banding. The complex carrying the interchanges is usually transmitted through the pollen. Certain chromosomes that have undergone more extensive change than the rest of the complement may have some special significance. There is evidence of small duplications within heterozygous genomes. Permanent hybridity in different organisms may have quite different origins, possibly initiated by major karyotype repatterning following the activation of transposons that generate chromosome breakage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00333994
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  • 5
    Electronic Resource
    Electronic Resource
    Characterization of the Nicotiana tabacum L. genome by molecular cytogenetics (1993)
    Springer
    Molecular genetics and genomics 240 (1993), S. 159-169 
    Details
    ISSN: 1617-4623
    Keywords: Nicotiana tabacum ; Amphidiploid-Molecular cytogenetics ; Intergenomic translocations ; Phylogeny
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Nicotiana tabacum (2n=48) is a natural amphidiploid with component genomes S and T. We used non-radioactive in situ hybridization to provide physical chromosome markers for N. tabacum, and to determine the extant species most similar to the S and T genomes. Chromosomes of the S genome hybridized strongly to biotinylated total DNA from N. sylvestris, and showed the same physical localization of a tandemly repeated DNA sequence, HRS 60.1, confirming the close relationship between the S genome and N. sylvesfris. Results of dot blot and in situ hybridizations of N. tabacum DNA to biotinylated total genomic DNA from N. tomentosiformis and N. otophora suggested that the T genome may derive from an introgressive hybrid between these two species. Moreover, a comparison of nucleolus-organizing chromosomes revealed that the nucleolus organizer region (NOR) most strongly expressed in N. tabacum had a very similar counterpart in N. otophora. Three different N. tabacum genotypes each had up to 9 homozygous translocations between chromosomes of the S and T genomes. Such translocations, which were either unilateral or reciprocal, demonstrate that intergenomic transfer of DNA has occurred in the amphidiploid, possibly accounting for some results of previous genetic and molecular analyses. Molecular cytogenetics of N. tabacum has identified new chromosome markers, providing a basis for physical gene mapping and showing that the amphidiploid genome has diverged structurally from its ancestral components.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00277053
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  • 6
    Electronic Resource
    Electronic Resource
    Characterization of a new family of tobacco highly repetitive DNA, GRS, specific for theNicotiana tomentosiformis genomic component (1995)
    Springer
    Chromosome research 3 (1995), S. 245-254 
    Details
    ISSN: 1573-6849
    Keywords: Nicotiana tabacum ; nucleosome positioning ; Progenitor-specific probes ; repetitive DNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Members of a new family of highly repetitive DNA sequences called GRS were isolated fromNicotiana tabacum L. genomic DNA and characterized. Cloned, sequenced monomeric units (180–182 bp) of GRS exhibit properties characteristic of molecules that possess a stable curvature. The GRS family represents about 0.15% of total genomic DNA (104 copies per haploid genome) and could be derived from eitherNicotiana tomentosiformis orNicotiana otophora, two possible ancestors of the T genome of the amphidiploidN. tabacum. Sequence homology between the HRS60 (Koukalováet al. 1989) and the GRS family has been estimated to be 57%.In situ hybridization was used to localize GRS on mitotic chromosomes. Hybridization signals were obtained on five pairs of chromosomes at intercalary sites of the longer chromosome arms. The majority of GRS sequences appeared to be organized in tandem arrays and a minority were found to be dispersed through the genome in short clusters, interspersed with other types of DNA repeats, including 25S rDNA sequences. Several loci containing both GRS and HRS60 were also found. Such hybrid loci may indicate intergenomic transfer of the DNA in the amphidiploidN. tabacum. GRS sequences, like HRS60 (Fajkuset al. 1992), were found to specify the location of nucleosomes. The position of the nucleosome core has been mapped with respect to a conservedMbol site in the GRS sequence and an oligo A/T tract is a major centre of the DNA curvature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00713050
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