Abstract
Cytogenetic parameters of mitosis were studied in the neural ganglions and imaginal disks of the third-instar Drosophila larvae of the marker lines ry506 and w; Cy/L; D/Sb; two wild-type lines Lausenne and Hikone-AW; and the v158 line mutant for the cell-cycle gene in the 85F locus. The control lines and their various tissues differ in a number of mitotic traits, which are believed to be the natural modifications of chromosome condensation and segregation and do not disturb homeostasis of the developing ry506, Lausenne, and Hikone-AW flies. Mutation v158 affects centromere disjunction. In imaginal disks, this results in arrest of either mitosis or anaphase initiation, whereas, in the neural ganglions, chromosomes integrate into a monopolar spindle at prophase and unipolar cells appear in anaphase. Different effects of the mutation in various tissues are assumed to be caused by different activity of the checkpoint system. When the mutation was maintained heterozygous for a long time, adaptive modification of its expression was observed. A comparison of the rates of two major and parallel mitotic processes, spindle formation and chromosome condensation, showed that adaptive modification can proceed via the adjustment of these rates.
