Protoplasmatologia: Kern- und Zellteilung. A. The chromosome complement, by B. John and K. R. Lewis. B. The chromosome cycle, by B. John and K. R. Lewis. C. Endomitose und endomitotische Polyploidisierung, von L. Geitler. D. Riesenchromosomen, von W. Beermann. E. Amitose. 1. Die Amitose der tierischen und menschlichen Zelle, von O. Bucher. F1. Meiotic system. F2. Les altérations de la méiose chez les animaux parthenogénétiques, par M. Narbel-Hofstetter. F3. Fortpflanzungsmodus und Meiose apomiktischer Blütenpflanzen, von A. Rutishauser. G. Der Kernteilungsmechanismus. 1. The behavior of centrioles

Protoplasmatologia: Kern- und Zellteilung. A. The chromosome complement, by B. John and K. R. Lewis. B. The chromosome cycle, by B. John and K. R. Lewis. C. Endomitose und endomitotische Polyploidisierung, von L. Geitler. D. Riesenchromosomen, von W. Beermann. E. Amitose. 1. Die Amitose der tierischen und menschlichen Zelle, von O. Bucher. F1. Meiotic system. F2. Les altérations de la méiose chez les animaux parthenogénétiques, par M. Narbel-Hofstetter. F3. Fortpflanzungsmodus und Meiose apomiktischer Blütenpflanzen, von A. Rutishauser. G. Der Kernteilungsmechanismus. 1. The behavior of centrioles
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Total Pages: 794
Release: 1968
Genre: Protoplasm
ISBN:
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The Chromosome Cycle

The Chromosome Cycle
Author: Bernard John
Publisher: Springer Science & Business Media
Total Pages: 132
Release: 2012-12-06
Genre: Science
ISBN: 3709155908
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neoessity for making it. Yet, clearly, the problem of development is largely one of filling "the vacuum between determinant and character" (DARLINGTON 1951). Nowadays the chromosome theory can be presented in much greater detail and with utter confidence, but its two main features remain the same. However, while the role of the chromosomes in heredity and development has been appreciated for a long time, the manner in which they perform their genetic and epigenetic functions has become amenable to critical investigation only in recent years. There is, therefore, still an unmistakable tendency to think of chromosomes in terms of the discrete threads of cell division and, in keeping with this conception, the chromosome cycle is gen erally considered in relation to the microscopically visible changes in morphology which occur during the mechanically active phases of mitosis and meiosis. Chromosome phenotype, however, changes not only during division but throughout the cell cycle. The changes which occur during interphase are, of course, scarcely revealed in morphological modifications of the restless "resting" nucleus. Consequently they are less obvious and correspondingly less amenable to investigation. This accounts for the concentration on the countable karyotype, with its visible properties of pairing and pycnosity, and the measurable movements of separation and segregation.

The Chromosome Complement

The Chromosome Complement
Author: Bernard John
Publisher: Springer Science & Business Media
Total Pages: 211
Release: 2012-12-06
Genre: Science
ISBN: 3709157811
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material can serve both autocatalytic and heterocatalytic functions. Thus not only is it unique in itB capacity for self-replication but its base sequence determines the specificity of proteins. And enzyme proteins are immediately responsible for the peripheral metabolism which enables the organism to impose its own kind of order on the raw materials it absorbs. The course of development is determined not only by the nature of the genetic material but by its over-all amount and the relative frequency of the different functional units. Differential rates of epigenetic activity matter also. In theory, therefore, differential development within or even between individuals could be determined by the differential replication of the various genetic elements or by their differential activity. And further variation could arise by the differential transmission of these elements between cells. Indeed it would appear that all these possibilities are exploited by living systems. If like is to beget like, however, any genetic change which occurs during development must be undone, or else germinal units preserved from change must be set aside. As far as is known, genetic changes, even those involving only quantity or relative amounts, are reversible to only a very limited extent so that a change once done cannot be undone. Consequently genetic changes during the development of presumptive germ-lines are either non existant or minor and confined to a small class of un aggregated deter minants.