. Cytology. Cytology. Figure 5-4. Schematic Representation of Plectonemic and Paranemic Coils Composed of Two Strands: (a) plectonemic coil made up of two interlocking strands which form a relational coil when the gyres are partially drawn out; (b) paranemic coil of two strands which are free to separate as independent units when straightened out. (From Sparrow, A. Huskins, C. L., and Wilson, G. B., 1941. "Studies on the Chromosome Spiralization Cycle in Trillium^ Can. J. Res., C, 19, Fig. 1. p. 325.) Prometaphase Following the breakdown or disappearance of the nuclear boundary, the c
. Cytology. Cytology. Figure 5-4. Schematic Representation of Plectonemic and Paranemic Coils Composed of Two Strands: (a) plectonemic coil made up of two interlocking strands which form a relational coil when the gyres are partially drawn out; (b) paranemic coil of two strands which are free to separate as independent units when straightened out. (From Sparrow, A. Huskins, C. L., and Wilson, G. B., 1941. "Studies on the Chromosome Spiralization Cycle in Trillium^ Can. J. Res., C, 19, Fig. 1. p. 325.) Prometaphase Following the breakdown or disappearance of the nuclear boundary, the chromosomes tend to aggregate in a central position in the cell. In plant cells, at least, this time corresponds to the first appearance of an organized spindle. Wilson and Hyppio (1955) considered this position- ing of the chromosomes to play an important role, both in the develop- ment and normal functioning of spindle organization. Motion pictures of the mitotic process (Bajer, 1957) would seem to indicate that pro- metaphase collapse is characteristic of normal mitoses in plant cells. Similar motion pictures such as those produced by Raymond Zirkle and his colleagues indicate that the. same is true for animal cells as well. Metaphase This is the stage of alignment of chromosomes on the equatorial plate, which is the midportion of the spindle apparatus. It appears to be the kinetochores which are particularly attracted towards this region. They MITOSIS AND MEIOSIS / 123. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Wilson, G. B. (George Bernard), 1914-; Morrison, John H. (John Herbert), 1927-. New York, Reinhold
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