ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • 1975-1979  (33)
Collection
Year
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 75 (1979), S. 215-234 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The position of specific constitutive heterochromatic chromosome regions within the elongated sperm nuclei of eight species of Anura was examined with Q- and C-banding. These species differ widely with regard to the number, size and position of the brightly fluorescing heterochromatic regions. The empirical frequency distributions determined for the heterochromatic regions relative to the longitudinal axis of the sperm nuclei were compared with random frequency distributions calculated on the basis of two spatial models. None of the specifically stained heterochromatic regions occupy any definite preferential position within the sperm nuclei. In two instances, a specific sequence of the heterochromatic regions within the sperm nuclei could be excluded. The type of chromosomal arrangement within the elongated sperm nuclei of Anura is discussed on the basis of the distribution patterns obtained.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 68 (1978), S. 131-148 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract In the chromosomes of 12 frog species of the suborder Diplasiocoela (Amphibia, Anura), the constitutive heterochromatin and the nucleolus organizer regions (NORs) have been specifically stained. On most of the chromosomes, aside from the centric heterochromatin, telomeric and interstitial C-bands were also found. The various C-bands display a very variable reaction to alkaline pretreatment; this indicates heterogeneity in the constitutive heterochromatin. Sex chromosomes could not be identified in any of the species studied. The number and chromosomal positions of the NORs vary quite strongly between species and between families. In 4 species of the genus Rana, there were, aside from the “standard-NORs” in chromosome pair 10, between 4 and 14 extra, small NORs detectable in the smaller chromosome pairs. As possible causal mechanism of these additional small NORs the reintegration of amplified rDNA during amphibian oogenesis is suggested. Q- or G-bands could only be recognized in mitotic prophase chromosomes. The strong spiralization of metaphase chromosomes prevents the differential demonstration of Q- or G-bands in the euchromatic regions.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 257 (1975), S. 795-797 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Adult Triturus alpestris, T. cristatus and T. vulgaris were captured from their natural habitat near Ulm, southwestern Germany; T. marmoratus was caught in southern France (Banyuls-sur-Mer) and Diemyctilus viridescens was obtained from a dealer. Four hours before they were killed, the animals ...
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Silver-staining in the nuclei and chromosomes of spermatogenesis of four species of mammals (Man, Mus musculus, Rattus norvegicus, and Cavia cobaya) was investigated qualitatively and quantitatively. These species show a very similar pattern of activity of the nucleolus organizer regions (NORs) during the various stages of spermatogenesis. Silver precipitates are detectable in growing spermatogonia and up until the pachytene stage of meiotic prophase. During the meiotic metaphases I and II and during interkinesis silver-stainability disappears completely. A resumption of silverstainability occurs in round spermatids indicating a postmeiotic reactivation of NORs. This process does not persist beyond the early elongation phase. The quantitative determination of the silver-covered areas in relation to the total nuclear areas reveals minor differences between the species investigated with regard to the times and extents of maximum activation. The known localizations of the NORs in the karyotypes of the species investigated was confirmed using metaphase-preparations derived from somatic tissues.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 58 (1976), S. 387-391 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract On the chromosomes of the rooster the constitutive heterochromatin (C-bands) is to be found for the most part at the centromeres. The position of the centric heterochromatin in spermatids and sperm is not randomly distributed. In early, round spermatids one heterochromatic block lies at this exact position on the membrane that develops into the tip of the sperm nucleus (acrosomal chromocenter). During the elongation of the spermatid nucleus another heterochromatic block comes to lie on the basal nuclear membrane. The other centromeres arrange themselves tandem-wise between the acrosomal and the basal chromocenters. Comparisons have been made between this specific arrangement and the location of chromosomes in the sperm of amphibians and mammalians.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 66 (1978), S. 361-388 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The distribution and quantity of constitutive heterochromatin and of the nucleolus organizer regions (NORs) on the chromosomes of 22 species of bufonids and hylids (Amphibia, Anura) was investigated. Three different kinds of constitutive heterochromatin were found and the frequency of brightly fluorescing heterochromatic regions was remarkably high. On almost all chromosomes there is centric and telomeric heterochromatin. Quantitative estimates of heterochromatin demonstrate that large DNA differences among closely related species can not be attributed to differing quantities of constitutive heterochromatin. In all species investigated, only one homologous pair of NORs was found, which lies preferentially in the proximal and interstitial segments of the long chromosome arms. The NORs are always associated with constitutive heterochromatin on both sides. The size variability between homologous NORs is very high. In the euchromatic regions of the metaphase chromosomes, neither Q- nor G-bands can be demonstrated; this can be attributed to an extremely strong contraction of the anuran chromosomes. On the basis of these results various mechanism of the chromosomal evolution in Anura are discussed.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 71 (1979), S. 29-55 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The distribution of constitutive heterochromatin on the chromosomes of Triturus a. alpestris, T. v. vulgaris and T. h. helveticus (Amphibia, Urodela) was investigated. Sex-specific chromosomes were determined in the karyotypes of T. a. alpestris (chromosomes 4) and T. v. vulgaris (chromosomes 5). The male animals have one heteromorphic chromosome pair, of which only one homologue displays heterochromatic telomeres in the long arms; the telomeres of the other homologue are euchromatic. This chromosome pair is always homomorphic and without telomeric heterochromatin in the female animals. There is a highly reduced crossing-over frequency between the heteromorphic chromosome arms in the male meiosis of T. a. alpestris; in T. v. vulgaris no crossing-over at all occurs between the heteromorphic chromosome arms. No heteromorphisms between the homologues exist on the corresponding lampbrush chromosomes of the female meiosis. In T. h. helveticus no sex-specific heteromorphism of the constitutive heterochromatin could be determined. The male animals of this species, however, already possess a chromosome pair with a greatly reduced frequency of chiasma-formation in the long arms. The C-band patterns and the pairing configurations of the sex-specific chromosomes in the male meiosis indicate an XX/XY-type of sex-determination for the three species. A revision of the literature about experimental interspecies hybridizations, gonadic structure of haploid and polyploid animals, and sex-linked genes yielded further evidence in favor of male heterogamety. The results moreover suggest that the heterochromatinization of the Y-chromosome was the primary step in the evolution of the sex chromosomes.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 56 (1976), S. 327-347 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract In early spermatids of Urodeles the chromosome segments bearing constitutive heterochromatin are localized in one half of the round nucleus; this region becomes the basal part of the long nucleus of the spermatozoon. The euchromatic chromosome segments extend toward the anterior nuclear pole in a bouquet configuration (Macgregor and Walker, 1973). In the course of spermiohistogenesis, one of the heterochromatic regions (the acrosomal chromocenter) migrates from the basal part to the anterior half of the spermatid nucleus. This heterochromatic block is identical with a species-specific, definite C-band in the karyotype. This relationship between the acrosomal chromocenter and a specific chromosomal C-band was established in Triturus cristatus, T. marmoratus, T. alpestris and Cynops pyrrhogaster. In closely related species this particular C-band lies on similar chromosomes. — While the spermatid nucleus still retains its round shape the acrosomal chromocenter despiralizes into a long heterochromatic thread (acrosomal thread). Precisely at the position of this thread the nucleus evaginates and acquires a pear-like shape. During the elongation of the nuclear protrusion the acrosomal thread remains associated with the anterior end. At termination of spermiogenesis it lies closely below the acrosome in the tip of the spermatozoon. Spontaneous aberrations which affect the acrosomal chromocenter or the thread lead to the development of spermatozoa with defective tips. — Several euchromatic segments, interspersed between the heterochromatic segments, can be recognized in the completely despiralized acrosomal thread. Genes responsible for the morphogenetic activities of both, the acrosomal chromocenter and the acrosomal thread, in the development of the spermtip, might be localized in these interspersed euchromatic segments. The existence in higher vertebrates of an acrosomal chromocenter or an equivalent chromosomal region is discussed.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Human genetics 〈Berlin〉 26 (1975), S. 47-59 
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Description / Table of Contents: Zusammenfassung Mit Hilfe der RNA-DNA-Hybridisierungsmethode wurden bei Mutter und Tochter mit dem Karyotyp 45,XX,t(15q21q) Anteile der ribosomalen DNA (rDNA) am Genom von 0,030% und 0,023% ermittelt. Der Ehemann und Vater der Tochter (46,XY) wies einen rDNA-Anteil von 0,022% auf. Die cytogenetische Detailanalyse der kurzen Arme der akrozentrischen Chromosomen bei diesen Probanden erlaubt die Deutung der Ergebnisse auf Grund der Größe der jeweils vorhandenen Nucleolusorganisatorregionen (NOR). Die Korrelation zwischen den biochemischen und den cytogenetischen Befunden zeigt, daß der Anteil der rDNA am Genom nicht in erster Linie eine Funktion der Anzahl akrozentrischer Chromosomen ist, sondern von der individuellen Kombination der im Bereich der NORs des Menschen existierenden Varianten abhängt.
    Notes: Summary The amount of ribosomal DNA (rDNA) was determined quantitatively by RNA-DNA hybridization in the genomes of a mother and her daughter, both with the karyotype 45,XX,t(15q21q). The saturation values found were 0.030% (mother), 0.023%(daughter), and 0.022% for the husband and father of the daughter. A detailed cytogenetic analysis of the short arms of the acrocentric chromosomes of these probands allowed the biochemical results to be interpreted in terms of the size of the individual set of nucleolus organizing regions (NORs) present in each proband. The correlation existing between the biochemical and the cytogenetic findings shows that the amount of rDNA in the human genome is not primarily a function of the number of acrocentric chromosomes, but depends on the individual combination of the variant NORs occurring in the human genome.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Human genetics 〈Berlin〉 38 (1977), S. 57-63 
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The Ag-AS method, developed by Goodpasture and Bloom (1975) stains transcriptionally active nucleolus organizer regions (NORs) on the chromosomes and in the interphase nuclei. Metaphases and interphase nuclei of early mouse embryos (unfertilized eggs, pronucleus stages, 2-, 4-, 8-cell stages, and morulae) were subjected to silver-staining. First staining of a single chromosome bearing an NOR was observed at the 2-cell stage. At the 4-cell stage 4–6 chromosomes, and at the 8-cell stage invariably all the 6 chromosomes known to bear NORs, respond positively to silver-staining. These results indicate that during mouse embryogenesis ribosomal RNA genes start to function at the 2-cell stage. The polar body does not respond to silver-staining, which supports the view that the polar body genome remains inactive.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...