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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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    Paper (German National Licenses)
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  • 2
    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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    Paper (German National Licenses)
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  • 3
    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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  • 4
    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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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Supernumerary chromosome segments in different genera of formicidae (1993)
    Springer
    Genetica 90 (1993), S. 17-29 
    Details
    ISSN: 1573-6857
    Keywords: C-bands ; Formicidae ; supernumerary chromosome segments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Supernumerary chromosome segments have been detected in natural populations ofTapinoma nigerrimum, Aphaenogaster senilis, Aphaenogaster iberica, Plagiolepis schmitzii, andPlagiolepis pygmaea. Chromosomal location, frequencies, response to C-banding techniques, and other aspects of extra segments are studied. Previous hypotheses about the chromosome differentiation processes between related species of the genusTapinoma are examined using this new cytogenetic information. The possible significance of the supernumerary chromosome segments in the process of chromosomal evolution in ants is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01435174
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    Paper (German National Licenses)
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