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  • 1
    Electronic Resource
    Electronic Resource
    Replication of the heterogeneous heterochromatin of the sex chromosomes ofMicrotus cabrerae (1992)
    Springer
    Cellular and molecular life sciences 48 (1992), S. 1151-1153 
    Details
    ISSN: 1420-9071
    Keywords: Constitutive heterochromatin ; Microtus cabrerae ; replication ; bromosubstitution ; sex chromosomes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract We used bromosubstitution to investigate the mode of replication of different types of heterochromatin located in the sex chromosomes ofMicrotus cabrerae. Our results clearly show that, although the heterochromatin is late replicating, the replication timing of different types of constitutive heterochromatin is related to their banding properties: R-type heterochromatin replicates before G-type heterochromatin, and this replication is asynchronous in both sex chromosomes. Furthermore, the late replication behaviour of the inactive X may spread to its constitutive heterochromatin. In some cells, a region of the constitutive heterochromatin of the late replicating X spontaneously switches to early replication, which may be related to transcriptional activity. Replication behaviour of the constitutive heterochromatin in the Y chromosome is similar to that of the late replicating X.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01948012
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  • 2
    Electronic Resource
    Electronic Resource
    Distribution of sister chromatid exchanges in different types of chromatin in the X chromosome ofMicrotus cabrerae (1996)
    Springer
    Cellular and molecular life sciences 52 (1996), S. 511-515 
    Details
    ISSN: 1420-9071
    Keywords: Sister chromatid exchanges (SCEs) ; Microtus cabrerae ; X chromosome ; chromatin structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract We used the X chromosomes ofMicrotus cabrerae as a model to analyze the distribution of sister chromatid exchanges (SCEs) on different types of chromatin, because of the marked heterogeneity of the heterochromatin in the entire short arm and a portion of the long arm of this chromosome. Computer-simulated distributions, according to an algorithm that makes it possible to modify the distribution on the basis of any possible hypothesis, were compared with real distributions by log-linear models. We found that the frequency of SCEs in different types of heterochromatin was higher than that expected for a random distribution, and located an SCE hot-spot at the junction between euchromatin and heterochromatin. The possible relationship between the distribution of SCEs and base composition or chromatin accessibility are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01969719
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  • 3
    Electronic Resource
    Electronic Resource
    The karyotype ofMicrotus cabrerae Thomas, another species with giant sex chromosomes (1979)
    Springer
    Cellular and molecular life sciences 35 (1979), S. 741-742 
    Details
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The karyotype ofMicrotus cabrerae, a species endemic to Spain, is described. It comprises 2n=54 chromosomes, with a ‘fundamental number’ of 64, and with very large sex chromosomes. An evolutionary relationship between this species andM. chrotorrhinus is suggested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01968216
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  • 4
    Electronic Resource
    Electronic Resource
    Recent evolution of NOR-bearing and sex chromosomes of the North African rodent Lemniscomys barbarus (1997)
    Springer
    Chromosome research 5 (1997), S. 481-485 
    Details
    ISSN: 1573-6849
    Keywords: chromosome banding ; meiosis ; NORs ; rDNA ; ribosomal cistrons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The karyotype and meiotic phases of Lemniscomys barbarus from Morocco were extensively studied with G- and C-banding, Ag-NOR and fluorochrome staining, in situ hybridization with an rDNA probe, and synaptonemal complex analysis. Comparison of the data with those previously published for an Algerian specimen revealed in the Moroccan specimens the presence of large heterochromatic segments in the sex chromosomes, a new nucleolar organizer at chromosome pair 1, and silent NORs on both sex chromosomes — features that are not present in the Algerian specimen. These findings demonstrate that during the very recent evolution of the karyotype of this species a new NOR was acquired by pair 1, possibly by amplification of ribosomal genes after a translocation event. This new NOR changed the preference of activatio n of the NORs in these individuals and became the preferentially activated NOR. Another autosome—sex chromosome translocation led to the presence of NORs on the sex chromosomes, which were then inactivated by the invasion of repetitive sequences. These silent NORs may be involved in the pairing of the two sex chromosomes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018473131446
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  • 5
    Electronic Resource
    Electronic Resource
    Development of silver stained structures during spermatogenesis in different genera of Formicidae (1990)
    Springer
    Genetica 81 (1990), S. 51-58 
    Details
    ISSN: 1573-6857
    Keywords: spermatogenesis ; nucleolar ; organizer regions (NORs) ; Formicidae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Development of silver stained structures during the spermatogenesis of Tapinoma nigerrlum, Pheidole pallidula, Tetramorium caespitum, Tetramorium semilaeve, Lasius niger and Plagiolepis schmitzii are studied. Nucleolar masses are only observed in early prophase. Obvious NORs are present in metaphase in all genera and species studied. However, there are no nucleolar Ag precipitates after metaphase. A resumption of silver stainability occurs in round spermatids. The majority of these genera present differential activity between the existing NORs. In T. nigerrimum there is primary or secondary NOR activity in all chromosomes of the complement, although there are interpopulation differences in relation to the NOR activity. In the remaining genera only certain chromosomes present NOR activity. Interpopulation genetic differences and environmental factors can cause differential activity of secondary NORs as observed in Tapinoma nigerrimum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00055236
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  • 6
    Electronic Resource
    Electronic Resource
    Fluorescence banding in four species of Microtidae: an analysis of the evolutive changes of the constitutive heterochromatin (1990)
    Springer
    Genetica 81 (1990), S. 11-16 
    Details
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Three different fluorochrome and specific counterstain combination (DAPI/AMD, DA/DAPI and CMA/DA) treatments were applied to the chromosomes of four Microtidae (Rodentia) species. The results complete the data obtained in our previous paper (Burgos, M., Jiménez, R., & Dìaz de la Guardia, R., Genome 30:540–546, 1988) and prove that the changes in the constitutive heterochromatin in the evolution of the karyotypes of these species are not only due to gain or loss of heterochromatin, but are qualitative with respect to their nucleotide composition, repeated base pair organization or DNA-protein complex modification. These variations lead to the differential response to the fluorescence dye combinations used.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00055231
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  • 7
    Electronic Resource
    Electronic Resource
    Comparative study of G- and C-banded chromosomes of five species of Microtidae (1986)
    Springer
    Genetica 78 (1986), S. 3-12 
    Details
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract G-banded karyotypes were compared in the following species of Microtidae: Microtus nivalis; M. cabrerae; M. arvalis and Arvicola sapidus. Previous observations on A. sapidus and A. terrestris (Díaz de la Guardia & Pretel, Caryologia 32: 183–189, 1979) were also incorporated in this study. The results show that Robertsonian translocations and pericentric inversions are common mechanisms involved in the karyotypic evolution of this group. Interspecific differences in C-banding patterns were also analyzed. Using the karyograph method (Imai et al., Am. Nat. 121: 477–488, 1983), the evolutionary distances of the karyotypes were estimated, and an attempt was made to establish a presumptive phylogenetic tree.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00058668
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  • 8
    Electronic Resource
    Electronic Resource
    Sex-chromosome pairing through heterochromatin in the African rodent Lemniscomys barbarus (Rodentia, Muridae). A synaptonemal complex study (2000)
    Springer
    Chromosome research 8 (2000), S. 277-283 
    Details
    ISSN: 1573-6849
    Keywords: inactive genes ; microspreads ; ribosomal cistrons ; SCs ; silent NORs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Giemsa-stained spread preparations and microspread preparations of Lemniscomys barbarus spermatocytes were made to investigate the meiotic behaviour of the peculiar sex chromosomes of this species. A typical sex vesicle is absent, as the X and Y chromosomes appear unfolded at zygotene and pachytene. In most cells, the sex chromosomes are associated at distal segments at metaphase I, probably as a consequence of a distal chiasma. The pairing segment is located in the heterochromatic regions of both sex chromosomes, which include silent ribosomal cistrons interspersed throughout the heterochromatin. This may suggest a possible involvement of ribosomal genes in both pairing and recombination processes. X–Y pairing proceeds beyond the pseudoautosomal region, thus involving heterologous segments of the differential regions, a fact that is clearly evident at the Y centromeric region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009233825758
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  • 9
    Electronic Resource
    Electronic Resource
    Autosomal and sex-chromosomal polymorphism in a wild population of the Norway rat, Rattus norvegicus (1981)
    Springer
    Genetica 56 (1981), S. 93-97 
    Details
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The karyotypes of 33 specimens of Rattus norvegicus captured in a wild population, were studied by means of conventional Giemsa staining and G- and C-banding methods. A chromosomal polymorphism for the presence or absence of extra segments in autosomes 3 and 12 and the X chromosome was found, beside a polymorphism for centromeric C-bands in pair no. 6. The frequency of different chromosome types found in this population was compared with that found in a wild population in Japan as well as with that found in some inbred strains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00055411
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  • 10
    Electronic Resource
    Electronic Resource
    Meiotic behaviour of sex chromosomes and polymeiosis in three species of insectivores (1984)
    Springer
    Genetica 65 (1984), S. 187-192 
    Details
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A study of male meiosis has been carried out on air-dried testicular preparations from three insectivore species: Crocidura russula, Neomys anomalus and Talpa occidentalis. Two particularities in relation to the meiotic process were found. The sex-chromosomes show a special allocycly. In the zygotene and pachytene stages, only some cells (a maximum of 50% in some individuals) present a typical sex-vesicle. In the majority of cells in these stages, the X-chromosome appears unfolded, isopycnotic or negatively heteropycnotic, with the ends of the arms together. The Y-chromosome is more condensed and it is associated with the ends of the X-chromosome. At diakinesis and metaphase I the sex chromosomes show end-to-end pairing. A second interesting feature in these species is the existence of spontaneous polymeiosis in a relative high frequency. The origin of this phenomenon, and the influence of these two particularities on fertility and the relation with the phylogeny of these species are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00122904
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