The movement of the chromosome is called anaphase A, and the extension of the poles is termed anaphase B.The mechanism of these movements are discussed below.
Chromosome movement: The forces responsible for the movement of the chromosomes are not still clear. One view suggests that the chromosomal microtubules generate the force for pole ward movement of chromosomes. These microtubules, progressively becomes shorter, and this separates and pulls the chromatids toward the poles of the spindle.Shortining may be brought about by active sliding between the chromosomal microtubules and the polar microtubules, or by reduction of the length of chromosomal microtubules through the separation of tubulin subunits at their tips .It has been experimentally shown that disassembly can generate sufficient force to pull the chromosomes to the poles. Also a spindle isolated from a cell about to divide contracts when ATP is added. Both the mechanisms play a role in shortening of the chromosomal microtubules.