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  • 1990-1994  (441)
  • 1950-1954  (115)
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  • 1
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Two BamHI families of repeated sequences were characterized from the genome of the Italian smooth newt, Triturus vulgaris meridionalis (Amphibia, Urodela). The first family, which is divided into subfamilies, consists of tandemly arranged arrays whose basic repeat is around 398 bp long; these arrays are dispersed throughout the entire chromosome sets of the various species of Triturus tested. Moreover the family is widely conserved among Salamandridae, being detected by genomic DNA blotting of Notophthalmus viridescens, Taricha granulosa, Salamandrina terdigitata and Euproctus platycephalus. The second BamHI family is represented by a cloned sequence of 419 bp, which is dispersed in the chromosome set of several species of Triturus. The sequence is also conserved in S. terdigitata and in E. platycephalus but is not detectable in N. viridescens or T. granulosa. The cloned sequence is most probably only part of a longer unit interspersed within the Triturus genome.
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  • 2
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A preparation technique for high resolution field emission scanning electron microscopy of plant chromosomes is described. The technique was optimized to use standard squash preparations of mitotic and meiotic chromosomes from root tips of barley, wheat, and rye. After light microscopic observation and documentation, the same object can be investigated with a 100-fold higher resolution using a field emission scanning electron microscope. Tilting of the specimens provides a three-dimensional insight into chromosomal structures at different stages of condensation and decondensation. With this technique it was possible to document for the first time at high resolution structures such as the centromeric region, the spindle apparatus and the spindle fibre attachment region. The smallest unit of the DNA packed that can be resolved is a “beads on a string”-like structure of the nucleofilament (10–15 nm fibre).
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  • 3
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract We found that 4′-demethylepipodophyllotoxinthenylidene-β-d-glucoside (VM-26; Teniposide), which specifically inhibits the enzyme DNA topoisomerase II, induces the formation of quadriradial chromosomes in Chinese hamster ovary cells. VM-26 traps topoisomerase II molecules when they are covalently integrated into DNA during their reaction. Quadriradial chromosomes are formed by reciprocal exchange of double-stranded DNA between single chromatids of two different chromosomes. Using synchronised cells, we found that they were formed after a single replication cycle in the presence of VM-26 at a low concentration (0.008μM), which does not affect DNA replication, and occurred in 50% of the mitotic cells at a concentration of 0.16 μM. They were also formed when VM-26 was present for only 1.5 h before mitosis, after the completion of S-phase DNA replication. Chromatids bearing a translocated segment of another chromatid, which were derived from recombined chromosomes, were observed in late metaphase cells. Segregation of the daughter genomes was defective in many mitotic cells, probably because chromatids with two or no centromeres and kinetochores, formed from chromosomes recombined between their centromeres, could not be segregated. In the light of evidence that topoisomerase II molecules covalently integrated in DNA are trapped and therefore more abundant in the presence of VM-26, and that this enzyme can effect recombination of double-stranded DNA in vitro, we interpret these observations as evidence that topoisomerase II can mediate chromosome recombination in vivo.
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  • 4
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract We isolated the nuclear matrix of proliferative meristematic root cells of Allium cepa bulbs and characterized it ultrastructurally and by one-dimensional SDS-polyacrylamide gel electrophoresis. The general organization of the nuclear matrix in onion root cells is similar to that found in other eukaryotes extracted under the same conditions. There are three main morphological components: the residual pore-lamina complex, the internal matrix and the residual nucleolus. The matrix has a fibrillo-granular structure composed of 5–10 nm fibrils and 20–25 nm granules. The residual protein matrix has a complex pattern, with several polypeptide bands of 12000 to 70000 Mr. The major bands have Mrs of 62000, 56000, 35000 and 27000.
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  • 5
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Chromosomal DNA methylation patterns were determined in the grasshopper Eyprepocnemis plorans by in situ digestion with MspI and HpaII. While no methylated regions were observed in standard chromosomes, the B chromosome was methylated in the distal third of its long arm. In this zone the B chromosome had an active nucleolus organizer region (NOR) in a male carrying a centric fusion between the B and the longest autosome, and it was not methylated. This NOR, however, was never observed in the active form in nonfused B chromosome, possibly because of methylation of this B chromosome region.
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  • 6
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The genome of Drosophila melanogaster contains a class of repetitive DNA sequences called the He-T family, which is unusual in being confined to telomeric and heterochromatic regions. The specific He-T fragment designated Dm665 was cloned in yeast by selection for an autonomously replicating sequence (ARS). Dm665 contains a restriction fragment length polymorphism (RFLP) that is specific to males and thus derives from the Y chromosome. Deletion mapping using X-Y translocations indicates that sequences homologous to Dm665 occur in at least one major cluster in each arm of the Y chromosome. Among 20 yeast artificial chromosome (YAC) clones containing Drosophila sequences homologous with Dm665, four clones derive from defined regions of the long arm of the Y and two from the short arm. The sequence of Dm665 is 2443 bp long, consists of 59% A+T, and contains no significant open reading frames or direct or inverted repeats. However, Dm665 contains a region of 650 bp that shares homology with portions of the X-linked locus Stellate.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 100 (1991), S. 139-146 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Conclusions The immunocytochemical “taxonomy” experiments cited above have identified a class of “chromosomal” antigens whose properties were not predicted by earlier models of mitosis. Our theory describing one possible explanation for the transfer of these antigens from the chromosomes to the spindle midzone at the metaphase: anaphase transition must now be subjected to further experimental tests. The phenotypes of cells microinjected with antibodies to passenger proteins should enable us to identify mitotic processes dependent on these proteins, as in the example of CHO1 antibody blocking mitotic progression (Nislow et al. 1990). In addition, the availability of cDNA clones and high titer antibodies may enable homologues of these components to be identified in organisms in which they can be subjected to genetic analysis. For the time being, we suggest that current views of the relative roles of chromosomes and cytoskeletal components in mitosis may require revision. Our hypothesis takes the current model for the role of the kinetochores in organizing the bipolar mitotic spindle (Kirschner and Mitchison 1986) a step further. The process of assembling a functional spindle and positioning the cleavage furrow may entail a degree of functional cooperation between chromosomes and cytoskeletal components far beyond that envisioned before now.
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  • 8
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The X1R chromosome of Drosophila miranda and the 3L autosome of Drosophila melanogaster are thought to have originated from the ancestral D chromosomal element and therefore may contain the same set of genes. It is expected that these genes will be dosage compensated in D. miranda because of their X linkage. To test these possibilities and to study evolution of the dosage compensation mechanism, we used the 3L-linked autosomal head-specific gene 507ml of D. melanogaster to isolate the homologous gene (507 mr) from a D. miranda genomic library. In situ hybridization showed that gene 507 is located at the 12A region of the X1R chromosome of D. miranda, indicating that the chromosomal homology deduced by cytogenetic means is correct. Restriction analysis and cross-specific DNA and RNA blot hybridization revealed the presence of extensive restriction pattern polymorphism and lack of sequence similarity in some areas of the 507 mr and 507 ml DNA, including the 3′ portion of the transcribed region. However, the 5′ portion of the transcribed region and the DNA sequences, located approximately 0.8 kb upstream and 3 kb downstream from the 507 ml gene showed a high degreee of similarity with the DNA sequences of comparable regions of the 507 mr gene. In both species gene 507 codes for a highly abundant 1.8 kb RNA which is expressed in the retina of the compound eye. Although in D. miranda the males have one and the females have two copies of the 507 gene, the steady-state levels of the 507 mRNA in both sexes were found to be similar, indicating that gene 507 is dosage compensated in D. miranda. Thus, along with the disparate rates of evolution in different areas of the DNA associated with gene 507, in D. miranda this gene has come under the regulation of the X chromosomal dosage compensation mechanism.
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  • 9
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract HSRs (homogeneously staining regions) are the cytological correlates of DNA amplification. In the house mouse, Mus musculus, many populations are polymorphic for the presence or absence of HSRs on chromosome 1. In the semispecies M. m. domesticus the amplified DNA is present within one HSR, whereas in M. m. musculus chromosomes 1 with two HSRs are found. Hybridization of HSR-specific probes to Southern blots of HSR-carrying genomic DNAs from different localities and semispecies revealed similar complex band patterns. the remaining variation is restricted to sequences with a low degree of amplification. Variation is higher between semispecies than within one semispecies. It is assumed that HSRs are derived from one original amplification event and that unequal recombination is the mechanism underlying the length variation of HSRs present today in both semispecies. Evidence from G-banding and in situ hybridization shows that the two HSRs of M. m. musculus originated from a single HSR by means of a paracentric inversion, where one break-point was located within the single HSR and the second outside the HSR. As a consequence of the paracentric inversion the two HSRs of M. m. musculus are permanently linked together. Since exchange of genes between the two semispecies is restricted to a narrow hybrid zone the amplification that gave rise to the HSR most probably occurred prior to the divergence into the semispecies M. m. domesticus and M. m. musculus about 1 million years ago.
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  • 10
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A 500 bp fragment of Drosophila genomic DNA containing 37 copies of the tetranucleotide GATA was used to probe, by Southern DNA blotting and in situ hybridization, two natural populations of the isopod crustacean Asellus aquaticus collected from the Sarno and Tiber rivers. This species does not have a recognizable sex chromosome pair. In a number of males from the Sarno population chromomycin A3 staining reveals a heteromorphic chromosome pair. The heterochromosome has two blocks of heterochromatin. After digestion of genomic DNA with six restriction endonucleases and hybridization with the GATA probe, the two populations exhibit different fragment length patterns. No sex-linked pattern was observed in either population. In situ hybridization to chromosomes of males and females from the Sarno population does not reveal any sex-specific pattern of labelling and indicates a scattered distribution of GATA sequences on most chromosomes with some areas of preferential concentration. The heterochromatic arcas of the male heterochromosome are not labelled.
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