Online ISSN : 1348-7019
Print ISSN : 0011-4545
Volume 3, Issue 3
Displaying 1-5 of 5 articles from this issue
    1932 Volume 3 Issue 3 Pages 221-249
    Published: June 30, 1932
    Released on J-STAGE: March 19, 2009
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  • A. B. STOUT
    1932 Volume 3 Issue 3 Pages 250-259
    Published: June 30, 1932
    Released on J-STAGE: March 19, 2009
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  • IV. Chromosome Number in Autobasidiomycetes
    1932 Volume 3 Issue 3 Pages 260-284
    Published: June 30, 1932
    Released on J-STAGE: March 19, 2009
    1. The nuclear phenomena in the basidium are typical in all the species in the Basidiomycetes examined.
    2. Mitotic spindle originates intranuclearly, and at each pole of it a centrosome is visible.
    3. Presynaptic stages, synaptic knot, diakinesis and other characteristic features of meiosis are observed in all the species examined.
    4. Normally a second division follows the first, its mode of division appearing to be equational.
    5. In Clavaria and also in Craterellus, the third division appears to take place in the basidium, resulting in the formation of eight nuclei.
    6. The chromosome numbers determined by the writer in 34 species of Basidiomycetes are given in the following list:-
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    1932 Volume 3 Issue 3 Pages 285-332
    Published: June 30, 1932
    Released on J-STAGE: March 19, 2009
    1. Of the two theories relating to the mechanism of crossingover, the loop or chiasma-type theory and the synapsis theory, the latter based upon the following four postulates is capable of explaining many relations which have been hardly intelligible in the loop theory.
    (a) Crossingover may occur at any point of the portion of the chromosomes which has undergone synapsis.
    (b) The process of crossingover is initiated at the distal or free end of the chromosomes and proceeds towards the proximal end.
    (c) Interference arises after one break has occurred, and it vanishes suddenly beyond a certain distance from the point of the original break.
    (d) Crossingover between sister strands is impossible.
    2. From the above postulates, it necessarily follows:
    (a) If one considers a chromosome as divided into many small joints and denotes the average number of joints over which interference extends by γ, the coincidence between two regions attains its maximum value at the joint γ+1 apart from the end of the first region, and it decreases gradually with distance (cf. Fig. 4).
    (b) In most cases, the maximum of coincidence can exceed 1.00, but as the first and the second regions become longer, it decreases gradually and falls below 1.00 at last.
    These two relations have been sufficiently proved by the experiments in D. virilis and D. melanogaster.
    3. A more plausible explanation than the loop theory can be given for the mechanism of crossingover in the V-shaped chromosomes on the basis of the two assumptions, viz., (1) one V-shaped chromosome is composed of two rod-shaped chromosomes united at their proximal ends; (2) synapsis is usually incomplete in the middle region of the V-shaped chromosomes.
    4. The theoretical results derived from these assumptions lead to the following relations: (a) As the frequency of incomplete synapsis increases the recombination value decreases markedly near the middle portion of the chromosomes, even if the length of the chromosome remains constant. (b) Coincidence between any two successive regions increases abruptly near the middle region of the chromosome, where it exceeds commonly 1.00. (c) Coincidence between one region and other regions reaches its maximum value at a certain distance from the former, then it oscillates off and on as the distance increases.
    These relations conform well with what have already been ascertained by experiments carried out by many previous investigators for the second and third chromosome in D. melanogaster.
    5. It has been found that the correction map of the V-shaped chromosomes illustrating the relation between the recombination and the standard values, may be different from that given by MORGAN and his co-workers. The new correction map has been tested and verified by using the data given by BRIDGES, REDFIELD and others.
    6. ANDERSON'S data on crossingover in attached X's case afford a valuable material for determining how far the synapsis theory is in harmony with the experimental results. Thus the following conclusions have been established:
    (a) Crossingpver occurs in a four-strands stage. (b) Crossingover involves only two of the four strands at any point of crossingover. (c) The first meiotic division in Drosophila females is reductional and the second is equational for the portion of the spindle-fiber attachment.
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    1932 Volume 3 Issue 3 Pages 333-336
    Published: June 30, 1932
    Released on J-STAGE: March 19, 2009
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