The Structure and Behavior of the Kinetochore During Meiotic Divisions inTrillium KamtschaticumPallas

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SUMMARYThe structure and behavior of the kinetochore during meiotic divisions were observed in microsporocytes of Trillium kamtschaticum using the acetocarmine squash method. The kinetochore region assumes a drumstick shape throughout metaphase-I to metaphase-II, and it consists of (1) the spherule, which has been referred to as the kinetochore, and (2) the chromonematic fibers, which connect the kinetochore with both arms of the chromosome. At metaphase-I the kinetochore region is stretched out on both sides of the bivalent. At this stage two adjacent kinetochores can be seen in each homologue, evidently representing the two sister kinetochores organized by the underlying duplicated chromatids. The sister kinetochores remain closely associated throughout anaphase-I to telophase-I, lying on the same side of each homologue. At metaphase-II the kinetochore region is again stretched out from the chromosome (dyad), and at this time the sister kinetochores still lie on the same side of the dyad. Thereafter, the two sister kinetochores can be seen lying separated on the opposite sides of the dyad. The kinetochore region undergoes a transition from a drumstick shape at metaphase-II to a conic or cylindrical configuration at metaphase-II, but on the other hand, no structural changes are found in the kinetochore region at the onset of anaphase-I. These results show that the kinetochores of the first meiotic chromosomes are structurally different from those of the second meiotic chromosomes in relation to the difference of the behavior between chromosomes in the two successive divisions.