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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 106 (1997), S. 276-283 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. The initiation and progression of homologous chromosome pairing at meiosis were investigated in female mice. The proximal end of the X chromosome was identified in fetal oocytes using fluorescence in situ hybridisation with the repeat copy probe 70-38. The X centromeres appeared to be randomly positioned in the nuclei from pre-meiotic interphase to leptotene. The observations indicated no pre-synaptic association for the proximal end of the X chromosome. There was a significant increase in the number of paired X centromeres from mid-zygotene to late zygotene. The proximal end of the X chromosome is therefore a generally late pairing region with no significant association seen before mid-zygotene. The centromeric heterochromatin of all chromosomes could be seen to associate into varying numbers of clusters during pre-leptotene through to pachytene. These clusters do not seem to be directly involved in bringing homologues together, as X centromeres did not consistently localise to the same cluster.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 107 (1998), S. 549-558 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. Two factors postulated to influence the meiotic behaviour of reciprocal translocations were investigated. Firstly, variation in the length of translocated and non-translocated segments was studied in male mice using four different rearrangements involving chromosomes 2 and 4. Secondly, sex-related effects were analysed through comparison of the meiotic behaviour of two translocations in male and female germ cells. In the first part of the study, primary and secondary spermatocytes of male mice carrying a translocation [T(2;4)1Ca, T(2;4)13H, T(2;4)1Sn, or T(2;4)1Go] were screened. Each rearrangement had different proportions of cells with ring and chain quadrivalents at metaphase I; the T(2;4)1Sn heterozygote also had a high rate (45%) of translocation bivalents. In general, the translocations had elevated chiasma frequencies in the rearranged chromosomes compared with structurally normal chromosomes 2 and 4, although the extent of the effect varied. Each rearrangement produced a different array of segregation products at metaphase II, reflecting their contrasting frequencies of multivalent configurations at metaphase I. Comparison of chromosome behaviour at metaphase I and II suggested that certain configurations tended to adopt particular orientations. However, it was also clear that such correlations were imprecise and that other factors, possibly the exact positions of chiasmata, also played a role in multivalent orientation. Two rearrangements, T(2;4)1Go and T(7;16)67H, were analysed in female mice. The frequencies of the various multivalent types at metaphase I differed from those in male carriers of these rearrangements owing to an increased chiasma frequency in oocytes in some of the pairing segments. Not surprisingly, the segregation products seen in metaphase II cells showed some differences from the pattern recorded in male germ cells. For T(2;4)1Go, the sex-related difference in segregation patterns resulted in a diminished expectation of genetically imbalanced gametes, although this was not the case for T(7;16)67H.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Sensory hair cells and their associated non-sensory supporting cells in the inner ear are fundamental for hearing and balance. They arise from a common progenitor, but little is known about the molecular events specifying this cell lineage. We recently identified two allelic mouse mutants, ...
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1546-1718
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Chromosomes from antigen stimulated B–cells from spleens of inbred mice have been separated using flow cytometry into 18 distinguishable peaks. Using locus–specific oligonucleotides and fluorescence in situ hybridization to banded metaphase spreads, 15 individual chromosomes were ...
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 102 (1993), S. 575-582 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The influence of X-autosome Robertsonian (Rb) translocation hemizygosity on meiotic chromosome behaviour was investigated in male mice. Two male fertile translocations [Rb(X.2)2Ad and Rb(X.9)6H] and a male sterile translocation [Rb(X.12)7H] were used. In males of all three Rb translocation types, the acrocentric homologue of the autosome involved in the rearrangement regularly failed at pachytene to pair completely with its partner in the Rb metacentric. The centric end of the acrocentric autosome was found regularly to associate either with the proximal end of the Y chromosome or with the ends of nonhomologous autosomal bivalents; the proportions of cells with such configurations varied between pachytene substages and genotypes. Various other categories of synaptic anomaly, such as nonhomologous synapsis, foldback pairing and interlocks, affected the sex chromosome multivalent in a substantial proportion of cells. In one of the Rb(X.12)7H males screened, an unusual, highly aneuploid spermatocyte that contained trivalent and bivalent configurations was found. Rb translocation hemizygosity did not appear to increase to a significant extent the incidence of X-Y pairing failure at pachytene, although the incidence was elevated at metaphase I in Rb(X.12)7H animals. Overall, a comparison of the frequencies and types of chromosome pairing anomalies did not suggest that these were important factors in the aetiology of infertility in males carrying the Rb(X.12)7H translocation.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1573-6849
    Keywords: chromosome painting ; fluorescencein situ hybridization ; meiosis ; mouse ; reciprocal translocation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Meiotic chromosome behaviour was investigated in male mice heterozygous for the translocation T(7;16)67H. At metaphase I, chain-of-four quadrivalents were present in approximately 80% of the spermatocytes; the bulk of remaining cells contained a ring quadrivalent, with only a few having either a trivalent plus univalent configuration or two bivalents. A low rate of non-disjunction, approximately 5%, was found through analysis of C-banded metaphase II spermatocytes. Using fluorescencein situ hybridization with differentially labelled whole chromosome paints, a wide array of segregation products were observed at metaphase II, depending on whether they arose from alternate, adjacent I, adjacent II orientation at metaphase I or were uninformative for alternative/adjacent I because of the presence of a chiasma in an interstitial pairing segment. Some 62% of the cells fell into this latter category, with only small proportions clearly arising through alternate (1.8%) or adjacent I (0.7%) orientations. Approximately 30% of the cells contained the products of adjacent II orientation. Consideration of the data suggested that most of these cells arose from metaphase I cells that contained a chain quadrivalent. Ring quadrivalents appeared predominantly to orientate in an alternate/adjacent I manner.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Chromosome research 3 (1995), S. 162-168 
    ISSN: 1573-6849
    Keywords: bromodeoxyuridine ; chiasma ; double crossovers ; locust
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The questions of whether closely spaced crossovers could be misidentified as single chiasmata or could cancel out each other and whether exchange could occur without chiasma formation were examined inLocusta migratoria. Monochiasmate bivalents that showed differential sister chromatid staining following bromodeoxyuridine incorporation were screened for their patterns of label distribution. Half of the chiasmata were associated with an exchange between dark and lightly stained chromatids, as expected if recombination involved any two non-sister chromatids chosen at random. Two variant types of label distribution were also seen: approximately 10% of all monochiasmate bivalents had an anomalous distribution of dark and light chromatids around the chiasma, and in three of the 1365 bivalents screened a second type of anomalous pattern was observed for the first time, in which all four chromatids had a label exchange at the chiasma. The observed incidence of the latter was considerably less than expected if they originated through a four-strand double crossover with closely positioned exchanges. Analysis of label distribution patterns in monochiasmate bivalents did not produce evidence of the other configurations expected if two closely spaced exchanges could be misidentified as single chiasmata or could cancel one another out so as not to form a chiasma. We conclude that analysis of chiasma frequencies and distributions offers an accurate means of assessing recombination in organisms with favourable cytology.
    Type of Medium: Electronic Resource
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