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  • 1970-1974  (619)
  • 1950-1954  (115)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 29 (1970), S. 462-473 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Swarming locusts show three physical criteria, i.e. the phase changes of melanisation of the nymphal stages or hoppers, of the proportions of certain body parts (morphometric ratios), and increased genetic recombination (meiotic chiasma frequencies) in the adult. The control of these changes, initiated by aggregation into swarms, i.e. gregarisation, seems to be vested in a pheromone which is produced by all hoppers in both the solitaria and gregaria phases, also by hoppers of the albino strain. Such a pheromone can be extracted from the locust room air and from the locust, these extracts showing high activity in bioassays, primarily in increased chiasma frequencies but also in hopper colour. The extract in risella oil is more efficient than that in petroleum ether and can be distilled to yield an active distillate. The pheromone is secreted in the faeces of hoppers but not of adults. There is evidence in faeces bioassays that all three physical criteria are affected; the pheromone may be called locustone. It is manufactured or secreted in a specific section of the alimentary canal, i.e. the crop. Reception is not through the antennae but through the stigmata. Preliminary chemical analysis of a risella oil air extract distilled into various other solvents showed the presence of a relatively simple saturated aliphatic chain with a carbonyl function, perhaps a ketone or an ester.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 3 (1950), S. 1-21 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. The pre-metaphase stretch is found to be a normal stage in male meiosis in six species of phasmids. 2. Its essential features are a precocious orientation of the kinetochores and their movement toward opposite poles of the developing spindle in first meiotic prophase, — with a consequent stretching of the chromosomes. It is followed by recontraction of the chromosomes and their movement to the equator. Attraction beween kinetochore and center, reinforced by the effect of elongation of the spindle, is considered responsible for the movements of the stretch. 3. The pre-metaphase stretch in phasmids differs from that of mantids in (1) its timing relative to meiotic stage, and (2) its expression in one species in the prophase of both meiotic divisions. 4. The distribution of the stretch in nature, and its significance for the mechanism of mitosis are discussed.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 29 (1970), S. 12-19 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Allium ampeloprasum cultivated in Kashmir is a tetraploid. The somatic complement of the cultivar consists of 32 median or submedian chromosomes, of which 8 have secondary constrictions. The tetraploid karyotype exhibits a great deal of heterozygosity which is taken as an evidence in support of the allopolyploid nature of the species. The tetraploid form is represented by the genomic formula AAA′A″. The three genomes show a great deal of similarity and are therefore taken to represent three varieties which have given rise to this cultivar through hybridity. — Despite this, no multivalents are formed by the species during meiosis. The shift from multivalent to bivalent type of pairing is attributed to the localization of chiasmata around the centromere. This type of chiasmata localization is a means adopted by some polyploid species to stabilize as diploids.
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  • 4
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The rate of DNA synthesis in the course of the division cycle in root meristem ofAllium cepa growing under constant temperature and aeration conditions has been studied by means of treatment with AdR, as a specific inhibitor of the synthesis, as well as by the incorporation of tritiated thymidine. The one-hour treatment with AdR or tritiated thymidine was given at various hours in the course of the interphase of a synchronous population of binucleate cells induced by caffeine. In the case of AdR, sensitivity to the inhibition of DNA synthesis was studied by recording the delays produced by the treatment in the appearance of biprophases and bitelophases. The selection by the use of caffeine, of spontaneously synchronous populations of cells going through the telophase and becoming binucleate and the detection of the first biprophases in the subsequent mitosis provide a highly synchronized system with which to study the incorporation of tritiated thymidine during the interphase. The curves representing sensitivity to the inhibition of DNA synthesis by AdR and the rate of tritiated thymidine incorporation coincide, so that we can regard the delays, under our conditions, as proportional to the rate of DNA synthesis at the moment of the AdR treatment. This rate, in the S period, was found to be variable by both methods, being higher in the first and the last thirds of the S period (S1 and S3) and lower in the middle third (S2).
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  • 5
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract When the chromosome aberrations induced in human leukocytes in culture with daunomycin (Dm) (0.015 μg/ml, with or without added arginine) are analyzed with respect to sites of breakage and reunion, non-randomness is observed, both between and within chromosomes. These results suggest either a site-specificity of action of the drug or site-specific sensitivity or both. Superficially, the data give an indication of the phenomenon of somatic crossing-over having occurred. However, if chromosome breakage and reunions of broken ends are considered as two events, independent of each other, the frequency of exchanges between homologues and apparent homologues is lower than the expected frequency in cases of groups involving chromosomes 6–12/X and 13/15 and almost equal to the expected frequency in cases of chromosomes 1, 2 and 3.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 29 (1970), S. 74-87 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Mammalian metaphase chromatin has been isolated by an ultrasonication technique and examined by both surface scanning and high-voltage electron microscopy (H.V.E.M.). By both techniques, rod-like structures 0.5 to 0.8 μ wide and varying in length from 3 to 5 μ were seen. Evidence is submitted that these represented parts of metaphase chromosomes. — By scanning microscopy the rods showed repeated patterns of wide and constricted areas. The constrictions were spaced 3,000 to 4,000 Å apart and the entire surface of the rods was covered with smaller rounded projections. In addition, longitudinal grooves were occasionally seen. — H.V.E.M. revealed gross folded and unfolded fibres whose sizes correlated with the surface projections seen by scanning microscopy. In addition, microfibrils, 20–40 Å in diameter were seen. The possibility that these fibrils represent the DNA co-helix is discussed.
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  • 7
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary It was demonstrated that actual breaks and reunions of chromatids occur regularly within meiotic chromosomes at the first metaphase. These breaks are inferred to have originated from the parallelization of the relational spiral and to give rise to crossing-over, as predicted earlier (Matsuura, 1940).
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 3 (1950), S. 357-392 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Zusammenfassung und Schluß 1. Nach den sehr zahlreichen aus der cytologischen Literatur vorliegenden Arbeiten besitzen die meiotischen Meta- und Anaphasechromosomen einen Doppelwendelbau. 2. Eigene Untersuchungen im Zusammenhang mit der Doppelbrechung der Chromosomen machten die Existenz einer solchen Struktur sehr unwahrscheinlich. Aus diesem Grunde wurde das Problem am klassischen Objekt der Tradescantia virginica eingehend studiert. 3. Die Kleinheit und Empfindlichkeit der Strukturen verlangte besondere Untersuchungsmethoden: Lebenduntersuchungen von PMZ im Phasenkontrastmikroskop waren ausschlaggebend für alle weiteren Präparationsmethoden. Sie zeigten, daß eine schonende Vorbehandlung der PMZ vor ihrer Fixierung zu einer klaren Darstellung der Chromosomenstrukturen von größter Wichtigkeit ist. PMZ-Ausstriche wurden in KE untersucht oder mit andern Mitteln fixiert, mit Kristallviolett gefärbt und zu Dauerpräparaten verarbeitet. Bei der Anwendung des Mikroskops wurde angestrebt, seine Leistungsfähigkeit möglichst auszunützen. Alle wichtigen Beobachtungen wurden mikrophotographisch festgehalten (zirka 2500 Aufnahmen). 4. Die Prüfung eines sehr umfangreichen lebenden und fixierten Untersuchungsmaterials ließ in Meta- und Anaphasechromosomen der ersten meiotischen Teilung den geforderten Doppelwendelbau nicht erkennen, dagegen wurden Ohromatiden mit Chromomeren beobachtet, die eine einfache, große Schraube bilden. Im Metaphasechromosom sind im ganzen vier Chromatiden als Fäden sichtbar; im Anaphasechromosom dagegen zwei Chromatiden, die aber ihrerseits bereits wieder in zwei Fäden gespalten sind (Halbchroniatiden). Die Richtigkeit dieser Beobachtung wurde bewiesen durch: a) das Verhalten der Chromatiden und Chromomeren in verschiedenen optischen Schnitten, mit spezieller Berücksichtigung der Schärfentiefe des Mikroskops; b) die Anwendung einseitig schiefer Beleuchtung, wobei das maximale Auflösungsvermögen und ein Azimuteffekt ausgenützt werden. 5. Der in der Literatur angegebene Doppelwendelbau wurde durch Untersuchung verschiedener Chromosomenartefakte zu erklären versucht. Dabei zeigte sich, daß Veränderungen auftreten, die bei unsachgemäßer Untersuchung als Kleinschrauben gedeutet werden können — bestmögliche Ausnützung der optischen Hilfsmittel und vorsichtige Auswertung der Beobachtungen ergab aber, daß auch diese Kunstprodukte niemals mit einem Doppelwendel zu verwechseln sind. 6. Mit vorliegender Arbeit ist eindeutig bewiesen, daß ein Doppelwendelbau, wie er für die meiotischen Chromosomen von Tradescantia bisher beschrieben worden ist, nicht existiert, daß dagegen in der einfachen Schraube Chromomeren wie in der frühen Prophase der ersten meiotischen Teilung vorhanden sind, die bei anderen Autoren zur Theorie des Doppelwendelbaues Anlaß gaben.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 3 (1950), S. 440-447 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Chromosoma 3 (1950), S. 447-447 
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
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