Observations on spermatogenesis in Drosophila

  • C. W. Metz
Article
Received:

Summary

  1. 1.

    Chromosome behavior during spermatogenesis is considered in several species ofDrosophila. The material is not favorable for detailed study. Perhaps the most favorable species isD. funebris; but since the genetic behavior of this species is not well known, others are used for the main account, supplemented by observations on funebris.

     
  2. 2.

    Homologous chromosomes undergo synapsis in the telophase of the last spermatogonial division, as in other Diptera, and apparently remain in intimate association during the growth stages.

     
  3. 3.

    The sex chromosomes remain relatively condensed and attached to or incorporated in the nucleolus, which shows wide divergence in size and appearance in different species.

     
  4. 4.

    The autosomes become diffuse at an early growth stage and are so indistinct that no account can be given of their detailed behavior. InD. funebris they form a granulated canopy or net-like cap at one side of the nucleus and arise in prophase by the condensation of this and coalescence of the granules.

     
  5. 5.

    No indications of definite threads such as seen during the leptotene and early diplotene stages of many insects and other animals are found here.

     
  6. 6.

    It is difficult to attach any positive significance to the chromosome behavior so far as the question of genetic crossing over is concerned.

     
  7. 7.

    The enormous growth of the spermatocytes brings into prominence many interesting cytoplasmic structures which have been noted here but not really studied, although they merit careful observation.

     
  8. 8.

    The nuclear wall remains intact at both divisions, permitting a distinction between cytoplasmic and nuclear components.

     
  9. 9.

    In some species numerous non-chromosomal bodies (fragments of nucleolus, cytoplasmic granules, etc.) stain deeply and sometimes bear a slight superficial resemblance to chromosomes, at the first division.

     
  10. 10.

    Both maturation divisions are normal as far as chromosome distribution is concerned — the first division being reductional so far as known (e. g. where dimorphic sex chromosomes are found).

     
  11. 11.

    At the first division the chromosomes tend to be drawn out and irregular in contour, especially when long and V-shaped. And they do not, as a rule, form a flat metaphase plate, save inD. obscura and its relatives. Figures are consequently best analysed in side view.

     
  12. 12.

    The second division is more nearly of the ordinary type and presents no special peculiarities.

     
  13. 13.

    The behavior of the sex-chromosomes in the first spermatocyte prophase is such as to permit their identification on this basis alone.

     
  14. 14.

    The evidence indicates that Y remains relatively dense and compact while X behaves more like the autosomes. This leads to the view that Y may remain relatively inert or passive while X is more active during the growth period.

     
  15. 15.

    X and Y appear to be connected only for a short region, or regions; from which it is inferred that they many be similar in constitution in these regions only.

     

Keywords

Growth Period Chromosome Behavior Genetic Behavior Polar View Early Prophase 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
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Copyright information

© Springer-Verlag 1926

Authors and Affiliations

  • C. W. Metz
    • 1
  1. 1.Department of Genetics Carnegie Institution of WashingtonCold Spring Harbor

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