Figure 5.

Bivalents can be induced to attach to the spindle with a single sister kinetochore facing each pole, but they neither attach nor separate in the normal meiosis II manner. Bivalents in unfused spermatocytes were micromanipulated. (A) One pair of sister kinetochores of the bivalent was induced to attach to opposite spindle poles (0 min, arrows). The chromosome remained, with stretched-out kinetochores, at the equator of the spindle after anaphase onset (6 min, arrows). 13 min after anaphase onset, the sister chromatids started to slowly separate from one another (19 min), moving towards the poles to which they were attached. (B) Another example of a bivalent in which one pair of sister kinetochores was induced to attach to opposite poles (0 min, arrows). In anaphase I, sister kinetochores were greatly stretched towards their spindle poles, but the sister chromatids did not separate from one another (4 and 17 min, arrows). (C) One pair of sister kinetochores of the bivalent was induced to attach to opposite poles (0 min, arrow), while the other pair of sister kinetochores attached to the same pole (0 min, arrowhead). In the pair that did attach to opposite poles, the sister chromatids did not separate from one another (27 and 32 min, arrows). The other pair of sister kinetochores attached to the lower spindle pole (0 and 27 min, arrowheads) and moved together to that pole in anaphase (27 and 32 min, arrowheads). Bar, 10 μm.