An assembly hypothesis of chromosome movement and the changes of the spindle length during anaphase I in spermatocytes of Pales ferruginea

Abstract

30 living first spermatocytes of the crane-fly Pales (Nephrotoma) ferruginea were photographed at intervals of 1 or 2 minutes throughout anaphase. In 11 cells the spindle length decreased in very early anaphase, in 4 cells it increased, and in the remaining 15 cells no significant changes occurred. There is a positive correlation between the decrease of spindle length during very early anaphase and spindle length at the beginning of anaphase (r = 0.40; P<0.05). During mid-anaphase the spindle length increased in all spermatocytes. The rate of length increase is again positively correlated with spindle length at the beginning of anaphase (r=0.47; P< 0.01). Nevertheless, the total length increase of spindles which have long axes at the beginning of anaphase, is not significantly higher than the length increase of those with short axes. This is so because the duration of spindle elongation is negatively correlated with spindle length at the beginning of anaphase (r=-0.39; P<0.05). In addition the duration of spindle elongation in mid-anaphase seems to be shorter the more the length of the spindle axes decreases during very early anaphase. The average velocity of the syntelically oriented chromosomes in early anaphase is positively correlated with the rate of the spindle elongation during mid-anaphase (r=0.66; P< 0.004). Both velocities are correlated with spindle length at the beginning of anaphase. An attempt was made to explain these phenomena on the basis of the assembly hypothesis of mitosis.