Some chromosomes in the rat do not have detectable levels of kinetochore proteins as determined by antikinetochore antibody, which may constitute a mechanism for the genesis of aneuploidy. An analysis of three mouse cell lines for the presence of kinetochore proteins showed that some chromosomes lacked these proteins, i.e. are akinetochoric by this criterion. This phenomenon may contribute to the variability of chromosome number that is characteristic of such lines. In some cells there appears to be en masse detachment of kinetochores. Several kinetochore-bearing chromosomes were also observed to be located peripherally to the spindle. These might be associated with the genesis of aneuploidy. In one cell line an apparently new phenomenon of nuclear budding was observed. In this case, one to several chromosomes appear to be pushed out of the nucleus in bud-like structures. These were surrounded by a nuclear membrane and appeared to detach from the main nucleus. Perhaps these structures eventually break off as micronuclei and, hence, would also be associated with the genesis of aneuploidy.
ABSTRACT Glycine max (soybean) is the only known higher plant with a definitely established occurrence of somatic crossing over. This material lends itself to the analysis of somatic crossing over, gross chromosomal aberrations and mutations, all of which may be induced by the same treatment of the mutagen given to seeds. This is made possible because gene Y11 for chlorophyll development in the variety L65-1237 is incompletely dominant over its allele y11, so that twin or double spots composed of a dark green (Y 11 Y 11)and a yellow (Y 11 Y 11) component can be observed adjacent to and as mirror images of each other on the light green Y 11 Y 11 leaves in the areas of complementary exchange for these genes. Lack of growth of either component of this double spot as well as several types of chromosomal disturbances give rise to single spots resembling phenotypes of Y 11 Y 11 or Y 11 Y 11 leaves. Point mutations can be studied by looking for green sectors originating from Y 11 Y 11 genotype on the Y 11 Y 11 plants. Seeds obtained from heterozygous plants were treated with caffeine, cytosine arabinoside, actinomycin D and 5-fluoro-deoxyuridine, all known inhibitors of DNA synthesis, and puromycin, an inhibitor of synthesis of proteins. The treatments with caffeine and actinomycin D increased the frequency of somatic crossing over as measured by the frequency of double spots on Y 11 Y 11 leaves, but cytosine arabinoside, 5-fluorodeoxyuridine and puromycin did not. Thus somatic crossing over was induced only by those chemicals which are known to allow rejoining of chromosomes, thereby suggesting a correlation between the two phenomena. These observations indicate that it is not the mere inhibition of DNA synthesis, but some rather more specific event in DNA repair which is responsible for complementary exchanges. Some of these results differ from studies carried out with fungi. The main effect of all chemicals tested, except caffeine and actinomycin D, was inferred to be the production of deletions in Y 11 Y 11 plants which raised the frequency of single (dark green or yellow) spots relative to the doubles. Caffeine was the only chemical which constantly increased the frequency of specific point mutations. In the control material, the great majority of spots are found on the upper surface of the leaf. This picture could not be changed in any of the treated materials, thus indicating uniform resistance of spongy mesophyll tissue to the mutagens applied.
