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  • 1
    Electronic Resource
    Electronic Resource
    The chromosome cycle of a primitive cecidomyiid — Mycophila speyeri (1960)
    Springer
    Chromosoma 11 (1960), S. 402-418 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. The chromosome cycle of the primitive cecidomyiid Mycophila speyeri has three features also found in more specialized cecidomyiids: a large number of chromosomes in the germ-line, chromosome elimination from future somatic cells, and chromosome elimination in spermatogenesis. However, sexual oogenesis lacks the unusual features found in other cecidomyiids, and instead there is normal chromosome pairing and segregation. The studies on male and female meiosis suggest that sexual progeny begin development with fewer chromosomes than their parents possessed, and therefore a compensatory increase in chromosome number probably occurs during early cleavage in sexual progeny. 2. Two cytologically distinguishable patterns of chromosome elimination in cleavage are described, one of which has not been reported previously. 3. The evolutionary origin of the cecidomyiid chromosome cycle is discussed in the light of these results. It is concluded that the essential innovation in the ancestral group was an increase in chromosome number, possibly by polyploidy, and that chromosome elimination in cleavage and spermatogenesis made possible the perpetuation of this elevated chromosome number. Modifications of oogenesis are viewed as secondary adaptions not present in the early cecidomyiid stock.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00328663
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  • 2
    Electronic Resource
    Electronic Resource
    A quantitative study of chromosomal elasticity and its influence on chromosome movement (1963)
    Springer
    Chromosoma 14 (1963), S. 276-295 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Chromosome elasticity and movement have been studied in living cells in two distinct situations: early anaphase stretch due to opposed external forces, and drag stretch — an elongation due to frictional resistance or drag on a chromosome being pulled toward one pole. Drag stretch provides a simultaneous display of both friction and elasticity and shows that chromosomes in living cells are elastic up to approximately six-fold increases in length. Neither early anaphase stretch nor drag stretch produce detectable alterations in the velocity of chromosome movement. A simple mechanical model is described which permits interpretation of this result for drag stretch: no matter how extensive, drag stretch should produce no change in the force required to maintain a given velocity of movement and hence should not alter movement velocity. Early anaphase stretch is a very different proposition, and additional assumptions leading to a quantitative model are necessary for its interpretation. Nevertheless it is reasonably certain that the amount of stretch actually seen in these circumstances would influence chromosome movement if the applied force were not increased over that necessary in the absence of stretch. It is concluded that the mitotic forces are continually adjusted to produce a standard velocity of movement even when an unusual hindrance to movement exists. The implications of this are considered, particularly in regard to the stretching and rupture of dikinetochoric (“dicentric”) bridges in anaphase. The quantitative version of the mechanical model for elasticity and movement can be applied to the drag stretch data, and permits calculation of the ratio between frictional and elastic coefficients. The chief assumptions are that the elasticity is Hookian, and the frictional resistance Newtonian in character. The model has not been critically tested, but it is consonant with existing data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00326816
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  • 3
    Electronic Resource
    Electronic Resource
    Chromosome micromanipulation (1967)
    Springer
    Chromosoma 21 (1967), S. 1-16 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The attachment of individual chromosomes to the spindle has been studied by micromanipulation in functionally normal grasshopper spermatocytes. Prometaphase to anaphase I chromosomes can be repeatedly stretched with a microneedle without much increase in the distance between the kinetochores and the poles. Individual chromosomes can, however, be displaced laterally (prometaphase-anaphase) or toward the pole (anaphase) without loss of spindle attachment and without greatly disturbing other chromosomes. It is concluded that chromosomes are firmly and individually attached to the spindle by chromosomal spindle fibers which are capable of bearing any normal mitotic load, including the stretching of dikinetic (dicentric) chromosomes in anaphase. Prolonged or severe manipulation can produce a small — three or four micron — increase in the kinetochore-to-pole distance. Anaphase motion continues normally in spite of lateral or poleward displacements or of small increases in the kinetochore-to-pole distance. In late anaphase, chromosomes can be displaced to the opposite pole. An unusual, rapid motion back toward the original pole follows such displacements, but repeated displacements eventually result in non-disjunction. No evidence for firm interzonal connections between anaphase chromosomes was obtained. Prometaphase and metaphase bivalents can be detached from the spindle by manipulations other than bivalent stretching, but half-bivalents in anaphase are never detached by these manipulations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00330544
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  • 4
    Electronic Resource
    Electronic Resource
    Chromosome micromanipulation (1967)
    Springer
    Chromosoma 21 (1967), S. 17-50 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The relationship of kinetochore orientation and reorientation to orderly chromosome distribution in anaphase has been studied experimentally by micromanipulation of living grasshopper spermatocytes. Bivalents or the X chromosome at prometaphase or metaphase I can be detached from the spindle with a microneedle and moved to any desired location within the cell. Following a pause of variable duration the detached chromosome invariably moved, kinetochores foremost, back to the spindle, reassumed its characteristic metaphase position, and, with one exception, segregated normally at anaphase I. Detachment from the spindle is demonstrated unequivocally (1) by manipulation evidence for the absence of the firm spindle connections seen both before detachment and after reattachment and (2) by a functional criterion: a given kinetochore, oriented to one pole before detachment, often orients to the opposite pole after detachment. The segregation in anaphase was always as expected from the final, post-operation, orientation. Reorientation and prometaphase and anaphase movement after detachment cannot be distinguished from their counterparts in control cells. Kinetochore position after detachment is the primary determinant of the pole to which that kinetochore will orient. Therefore, since the experimenter determines kinetochore position, he can cause any given half-bivalent to segregate to a predetermined pole at anaphase I. Similarly, orientation of both half-bivalents to the same pole can be induced. These mal-oriented bivalents invariably reorient and normal anaphase segregation ensues. Non-disjunction can, however, be produced directly in late anaphase. These experiments are based upon current views of orderly chromosome distribution; their success confirms our understanding of the fundamental orientation process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00330545
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  • 5
    Electronic Resource
    Electronic Resource
    The non-random chromosome segregation in spermatocytes of Gryllotalpa hexadactyla (1968)
    Springer
    Chromosoma 24 (1968), S. 324-335 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Males of Gryllotalpa hexadactyla have 22 autosomes and one X chromosome in their chromosome complement. One pair of autosomes forms a heteromorphic bivalent in meiosis: one dyad is several times the size of the other. At metaphase of the first meiotic division the large dyad and the X chromosome are invariably oriented to the same pole, and they move to this pole in anaphase. These earlier observations (Payne, White) have been confirmed by studies on living spermatocytes, and a preliminary experimental analysis by micromanipulation has been made. No physical connection between the X chromosome and the heteromorphic bivalent could be detected when either one was moved with a microneedle. When the X chromosome was detached from the spindle in prometaphase and brought to the other pole, it oriented to this pole, but it usually reoriented and moved back to the original pole. When the heteromorphic bivalent was detached from the spindle and its position inverted, the large and the small dyads oriented to the new poles. The heteromorph remained in inverted position but the X chromosome usually reoriented and moved to the pole to which the large dyad was now oriented. When the heteromorph was detached and taken out of the cell, the X chromosome reoriented and moved to the other pole, reoriented again and moved back to the original pole. When the X chromosome was detached and taken out of the cell the heteromorph did not show any reaction. It is concluded that the X chromosome's reorientation response is the critical factor in non-random segregation in Gryllotalpa.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00336200
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  • 6
    Electronic Resource
    Electronic Resource
    Electron microscopy of the spindle in locally heated cells (1979)
    Springer
    Chromosoma 74 (1979), S. 39-50 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Individual living cells in metaphase were exposed to a steep temperature gradient by placing a microheater near one spindle pole. The cells were then fixed and the spindle was examined by electron microscopy. The structure of the warmer half-spindle differed from the cooler half-spindle in several ways. Kinetochore microtubules were nearly parallel in the warmer half-spindle but were divergent in the cooler. The total length of microtubules in the warmer half-spindle was 52 per cent greater and the number of kinetochore microtubules per kinetochore averaged 16 per cent higher than in the cooler half-spindle. The warmer half-spindle was longer than the cooler. These observations clearly demonstrate a locally enhanced assembly of microtubules in the warmer half-spindle. The electron microscope study makes still clearer the unusual character of chromosome movement in the differentially heated cells: the structure of the warmer half-spindle is hard to distinguish from that in normal cells, yet chromosome movement there is far slower than normal (Nicklas, 1979).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00344481
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  • 7
    Electronic Resource
    Electronic Resource
    'Anaphase' and cytokinesis in the absence of chromosomes (1996)
    [s.l.] : Nature Publishing Group
    Nature 382 (1996), S. 466-468 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Spermatocytes of the grasshoppers Chortophaga australior and Melanoplus sanguinipes have eleven bivalents and an X chromosome. Although chromosomes are required for spindle assembly in these cells9, once a spindle forms, the absence of chromosomes does not affect the integrity of the spindle8. We ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/382466a0
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  • 8
    Electronic Resource
    Electronic Resource
    An experimental and descriptive study of chromosome elimination in Miastor spec. (Cecidomyidae; Diptera) (1959)
    Springer
    Chromosoma 10 (1959), S. 301-336 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. The descriptive cytology of chromosome elimination has been reinvestigated. The results show that most of the eliminated chromosomes are definitely not homologous with the somatic chromosomes. 2. Evidence from both descriptive and experimental sources shows beyond doubt that the errant feature of the chromosomes eliminated is a failure in the production of normal mid-anaphase tension. Interlocking or sticking of daughter chromatid ends is only rarely if ever responsible for chromosome elimination in the Cecidomyidae. 3. The normal amount of DNA is synthesized just prior to chromosome elimination, and hence no alteration in the normal DNA relationships is involved in the chromosomal behavior here. The distribution of RNA, protein and polysaccharides has also been studied; nothing to indicate their direct involvement in chromosome elimination was detected. 4. Centrifugation studies provide support for the hypothesis that in the cecidomyids chromosome elimination is a largely autonomous act of the chromosomes — it can be prevented but not initiated by cytoplasmic factors. Nucleocytoplasmic interaction therefore will account for the limitation of elimination to only the future somatic nuclei, by permitting normal division of the primordial germ-cell chromosomes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00396576
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  • 9
    Electronic Resource
    Electronic Resource
    Mitotic forces control a cell-cycle checkpoint (1995)
    [s.l.] : Nature Publishing Group
    Nature 373 (1995), S. 630-632 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The spermatocytes of praying mantids are prime examples of cells with a cell-cycle checkpoint sensitive to a single misguided chromosome. The spermatocytes normally contain a sex-chromosome trivalent formed from the pairing of a Y chromosome with two different X chromosomes, X! and X2, (Fig. 1; ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/373630a0
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  • 10
    Electronic Resource
    Electronic Resource
    Orientation and segregation of a micromanipulated multivalent: Familiar principles, divergent outcomes (1992)
    Springer
    Chromosoma 101 (1992), S. 399-412 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract We studied the orientation and segregation of a particular quadrivalent in living grasshopper spermatocytes. Quadrivalents were detached from the spindle by micromanipulation, then placed and bent as desired. The detached quadrivalents reattach and orient on the spindle. Their orientation is determined by the same principles that apply to ordinary chromosomes in mitosis and meiosis, but the outcome is different. Certain characteristics of the quadrivalent lead to a variety of orientations rather than the single one typical of ordinary chromosomes. Two kinetochores in the quadrivalent are linked to the others by unusually long, flexible chromosome arms. These kinetochores may face either the same pole or opposite poles and tend to orient initially to the pole toward which they face. Consequently, the initial orientation of the flexibly linked kinetochores is variable, and, moreover, they frequently reorient. In contrast, the other two kinetochores are as rigidly connected as those in a small bivalent and so display the typical back-to-back arrangement. Usually, this arrangement leads quickly to a stable orientation of the two kinetochores to opposite poles. Sometimes, however, the back-to-back arrangement changes to a side-by-side arrangement so that the orientation of both kinetochores to the same pole is favored. The combined effect of this diverse behavior is that the quadrivalent has four stable orientations, each leading to a different distribution of chromosomes in anaphase. The result is genetic chaos. Ironically, this chaos is produced by the same mechanisms that, in ordinary bivalents and mitotic chromosomes, produce a single stable orientation and genetically appropriate chromosome distribution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00582834
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