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  • 1
    ISSN: 1546-1718
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Post-translational modifications of histone amino termini are an important regulatory mechanism that induce transitions in chromatin structure, thereby contributing to epigenetic gene control and the assembly of specialized chromosomal subdomains. Methylation of histone H3 at lysine 9 ...
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 413 (2001), S. 565-565 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Sir Fabio Salamanca in his Correspondence “Keeping Mendel in mind” (Nature 412, 118; 2001), responding to the News story “Museum suffers spiritual cramps over Mendel's work” (Nature 410, ...
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  • 3
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Non-isotopic high resolution in sity hybridization was applied to cytological preparations of sporulating yeast cells. Ribosomal DNA (rDNA) and chromosome V-specific recombinant lambda clones were used to tag individual chromosomes and chromosome subregions. This allowed the study of chromosome behaviour during early meiotic prophase. It was found that chromatin becomes condensed and homologous DNA sequences then appear to become aligned prior to synaptonemal complex formation.
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  • 4
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A tandemly repetitive sequence family (AbS1) and a repetitive sequence (Hd) forming part of a larger dispersed element (dorf-1) ofAnemone blanda were characterised. TheAbS1 satellite sequence family is located in all 4′,6-diamidino-2-phenylindole (DAPI) positive intercalary heterochromatic bands and in the DAPI positive heterochromatic terminal region of chromosome 3, while the dispersedHd homologous sequences are preferentially associated with euchromatic chromosome regions. The major component of theAbS1 satellite isAbS1-H1 with a basic repeat unit of 1640 bp; a minor fraction (AbS1-H5) consists of 320 bp units. A subsection of theAbS1-H1 repeat unit exhibits homologies to the 25S rRNA gene of flowering plants suggesting that the 1.64 kb satellite was generated by amplification of a precursor satellite and/or single copy sequence together with an rDNA fragment. The rDNA homologous region is considered to evolve at a rate similar to pseudogenes and thus the age of this satellite DNA fraction can be roughly estimated as about 27 million years. The dispersed repeated sequenceHd (about 1300 bp) is associated with the 8 kb elementdorf-1. A. blanda dorf-1 constitutes about 0.2% of the genome (3×104 copies), is bounded by identical long terminal repeats, and exhibits partial homology to theLilium gypsy-type elementdell, but has yet to be confirmed as a retrotransposon. In contrast to theAbS1 satellite sequence family,Hd homologous sequences were found not only inA. apennina, the closest relative ofA. blanda, but also inA. nemorosa andA. ranunculoides indicating that a progenitor sequence ofdorf-1 was present in a common ancestor before speciation ocurred.
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  • 5
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Comparative fluorescence studies on the chromosome of ten species of acridid grasshoppers, with varying amounts and locations of C-band positive heterochromatin, indicate that the only regions to fluoresce differentially are those that C-band. Within a given species there is a marked tendency for groups of chromosomes to accumulate heterochromatin with similar fluorescence behaviour at similar sites. This applies to all three major categories of heterochromatin — centric, interstitial and telomeric. Different sites within the same complement, however, tend to have different fluorescence properties. In particular, centric C-bands within a given species are regularly distinguishable in their behaviour from telomeric C-bands. Different species, on the other hand, may show distinct forms of differential fluorescence at equilocal sites. These varying patterns of heterochromatin heterogeneity, both within and between species, indicate that whatever determines the differential response to fluorochromes has tended to operate both on an equilocal basis and in a concerted fashion. This is reinforced by the fact that structural rearrangements that lead to the relocation of centric C-bands, either within or between species, may also be accompanied by a change in fluorescence behaviour.
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  • 6
    ISSN: 1432-203X
    Keywords: Transgenic Arabidopsis ; Ploidy ; Pollen size
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Cytogenetic examination of transgenic Arabidopsis thaliana (L.) Heynh. plants obtained by Agrobacterium-mediated gene transfer to cotyledon- and root-explants or by direct gene transfer into protoplasts revealed a high percentage of tetraploid or aneuploid transformants. Depending on the transformation procedure used, 13% (root explant transformation), 33% (cotyledon explant transformation), or 38% (direct gene transfer) of the transformants showed aberrant ploidy levels. A good correlation between the ploidy level of a plant and the size of its pollen grains was observed. This allows quick and simple testing of the ploidy level of transgenic Arabidopsis plants.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 64 (1977), S. 117-124 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A distinct reverse (R-) banding pattern was produced on human chromosomes by digesting chromosome spreads with pancreatic deoxyribonuclease I (DNase I) in the presence of an excess of chromomycin A3 (CMA), followed by staining with Giemsa. The banding pattern corresponds with that obtained by chromomycin A3 fluorescence, and bands which fluorescence brightly with chromomycin appear darkly with Giemsa. The same relationship was observed in two plants, Scilla siberica and Ornithogalum caudatum, which have contrasting types of heterochromatin. Chromomycin bright C-bands stained darkly with the CMA/DNase I technique, whereas chromomycin negative C-bands appeared lightly stained. The digestion patterns are thought to reflect the variation in chromomycin binding capacity along the chromosome with R-bands and dark C-bands being sites which preferentially bind the antibiotic.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 40 (1973), S. 307-320 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Simple Giemsa staining techniques for revealing banding patterns in somatic chromosomes of plants are described. The value of the methods in the recognition of heterochromatin was demonstrated using five monocotyledonous and two dicotyledonous species. In Trillium grandiflorum the stronger Giemsa stained chromosome segments were shown to be identical with the heterochromatic regions (H-segments) revealed by cold treatment. Preferential staining of H-segments was also observed in chromosomes from three species of Fritillaria and in Scilla sibirica. Under suitable conditions the chromosomes of Vicia faba displayed a characteristic banding pattern and the bands were identified as heterochromatin. The Giemsa techniques proved to be more sensitive than Quinacrine fluorescence in revealing a longitudinal differentiation of the chromosomes of Crepis capillaris, where plants with and without B-chromosomes were examined. Again all chromosome types had their characteristic bands but there was no difference in Giemsa staining properties between the B-chromosomes and those of the standard complement.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 58 (1976), S. 307-324 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Two DNA binding guanine-specific antibiotics, chromomycin A3 (CMA) and the closely related mithramycin (MM), were used as chromosome fluorescent dyes. Root-tip metaphase chromosomes of three plant species and human metaphase chromosomes were sequentially stained with CMA or MM and the DNA binding AT-specific fluorochrome 4′-6-diamidino-2-phenylindole (DAPI). In some cases a non-fluorescent counterstain was used as contrasting agent: methyl green in conjunction with CMA, and actinomycin D (AMD) in combination with DAPI. — In all three plant species, Vicia faba, Scilla siberica, and Ornithogalum caudatum, the nucleolus organiser regions and/or associated heterochromatin displayed very bright fluorescence with CMA and MM and, in general, heterochromatic segments (C-bands) which were bright with CMA and MM were pale with DAPI whereas segments which were dim with CMA and MM displayed very bright fluorescence with DAPI. — Human metaphase chromosomes showed a small longitudinal differentiation in CMA fluorescence, which was essentially the reverse of the banding pattern obtained with AMD/DAPI double-staining, but of lower contrast. The CMA-banding pattern appears to be similar to the pattern found by R-banding procedures.
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  • 10
    ISSN: 1573-5028
    Keywords: Arabidopsis thaliana ; rDNA ; intergenic region ; spacer heterogeneity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A new heterogeneity of the rDNA spacer of Arabidopsis thaliana, resulting from variation in copy number of the so-called ‘C’ repeat located downstream of the presumptive polymerase I promoter, is reported. Variation is shown to occur within and between ecotypes. PCR analysis and sequence comparison suggests that the observed length heterogeneity is due to homologous recombination.
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