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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
    A substance secreted by rat Sertoli cells induces feminization of embryonic chick testes in vitro (1994)
    Springer
    Anatomy and embryology 189 (1994), S. 531-537 
    Details
    ISSN: 1432-0568
    Keywords: Embryonic chick gonad ; Sertoli cell ; Differentiation ; In vitro feminization ; Sex-specific antigen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Male and female gonads from 7- to 9-day-old chick embryos were cultured for 6 days in Sertoli cell-conditioned medium or in serum-free medium to investigate the possible effect of substances secreted by rat Sertoli cells on chick gonad development. Histological analysis showed that whereas all female gonads proceed through normal ovarian development in both culture media, most of male gonads showed clear feminization only when cultured in Sertoli cell-conditioned medium; male gonads cultured in serum-free medium developed as normal testes. Because the only substance detected in our conditioned medium with the potential to cause these effects was sex-specific antigen (Sxs), our results provide further evidence that Sxs antigen may play a role in sexual differentiation in birds, and probably in mammals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00186826
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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    Karyotype and centric dissociation in water voleArvicola sapidus spp.sapidus Miller 1908 (Rodentia, Muridae) (1978)
    Springer
    Cellular and molecular life sciences 34 (1978), S. 706-708 
    Details
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary After being analyzed for the first time with modern techniques, we offer a detailed description of a normal karyotype of the speciesArvicola sapidus ssp.sapidus Miller 1908. A centric fission is described in an individual with abnormal chromosome number (2n=41).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01947271
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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Chromosomal polymorphism, caused by pericentric inversions in Rattus rattus ssp. frugivorus (Raf.) from the south-east of the Iberian Peninsula (1980)
    Springer
    Genetica 51 (1980), S. 103-106 
    Details
    ISSN: 1573-6857
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00133508
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  • 8
    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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  • 9
    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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  • 10
    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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