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Human  Mitotic Chromosomes
by F.Ruzicka


Introduction
   In spite of many previous efforts, the ultrastructural organization of chromosomes is still not fully understood. As long as the knowledge of the ultrastructure of chromosomes remains incomplete, it will not be possible to understood their complex functions. Such knowledge will be especially important in interpreting pathological changes.

G-band technique
  We were interested in examining chromosomes by a combination of both light and electron microscopic techniques in order to determine the changes occurring during the various stages of banding technique.
   We found that G-band regions have a higher contrast in the transmission electron microscope (TEM) because of the thickness and close arrangement of the fibrils in these regions.
   A comparison of the appearance of chromosomes after the different staining steps shows that before the banding technique primary and secondary coils are clearly visible. These coils are disturbed after the first step- namely treatment with NaOH, and a fibrillar ultrastructur of the chromosomes is only apparent after the final step, staining with Giemsa.
   The exact reproducibility of these G-bands suggests that they are real structures, and therefore that the relationship between the spiralisation pattern and the position of heterochromatin within the chromatid must remain constant.
    Our results strengthen the assumption that some of the secundary coils fuse to form the bands.

Chromosome model
  From the above findings, the following three groups of structures may be distinguished:
1. A molecular level comprising the DNA double helix and attached histones and acid proteins (ny-bodies)
2. Fibrils or bundles of fibrils as well as the position of the DNA-helix in the fibrils.
3. The spiral organisation of the chromatids.

   


F.Ruzicka: Eine Methode zur Darstellung bestimmter Mitosen im Licht-und Elektronenmikroskop - ein Zielpräparationsverfahren. Mikroskopie 29, 109-115, 1973
F.Ruzicka: Über die Primärwindungen menschlicher Chromosomen. Humangenetik 20, 335 - 341, 1973
F.Ruzicka: Organisation of Human Chromosomes. Humangenetik 23, 1 - 22, 1974
F.Ruzicka et al.: The Ultrastructure of Human Mitotic Chromosomes and Interphase Nuclei Treated by Giemsa Banding Techniques. Chromosoma 46, 443 - 454, 1974
F.Ruzicka et al.: Electron Microscopy of Human Banded and Prematurely Condensed Chromosomes. In: Chromosomes Today 5, 227 - 234. John Wilby & Sons New York - Jerusalem 1976
F.Ruzicka: G-Banding of Chromosomes. In: Principles and Techniques of Electron Microscopy (ed. Hayat) 144 - 162, Van Nostrand Reinhold Company New York - Cincinnati - London - Atlanta - Toronto - Dallas - San Francisco 1977