The stage following meta-phase in nuclear division, during which separation of either chromatids or homologous chromosomes commences. In * mitosis and in the second division of * meiosis daughter chromatids are seen to move apart towards opposite poles of the spindle. Although the nature of the forces operating to initiate this separation is as yet unknown, two processes within the spindle, both probably involving microtubule activity, are believed to contribute to chromatid movement. The first is the elongation of the spindle fibres in the equatorial region between the chromatids. The spindle eventually doubles in length. The second is the shortening of the fibres attached to the *kinetochores in the centromeric regions. This is thought to be due to de-polymerization of tubulin in the constituent microtubules at the ends nearest to the poles. In anaphase of the first division of meiosis, the homologous chromosomes of each bivalent, each with a complete centromere, become separated and move towards opposite poles of the spindle. |
