[Campbell Biology P.290] Considering the 'WHAT IF?' scenario in Figure 12.9, if 'reeling in'... | Practice Question

Considering the 'WHAT IF?' scenario in Figure 12.9, if 'reeling in' at the poles was the main cause of chromosome movement during anaphase, how would the non-fluorescent mark and the microtubule portions on either side of it have changed relative to the poles?

  • A: The mark would have moved poleward with the chromosomes, and the microtubule segments on the spindle pole side of the mark would have shortened, while those on the kinetochore side would have stayed the same length.
  • B: The mark would remain stationary relative to the spindle pole, and only the microtubule segments on the kinetochore side would shorten.
  • C: The mark would move towards the kinetochore, and both sides of the microtubule segments would shorten evenly.
  • D: The mark would remain stationary relative to the kinetochore, and the entire microtubule would lengthen as chromosomes move poleward.

Explanation

If 'reeling in' at the poles were the primary mechanism, it would imply that depolymerization occurs at the spindle pole ends. The non-fluorescent mark was placed between the pole and the chromosome. As the chromosome is pulled towards the pole i.e., the mark moves poleward with the chromosome , the microtubule segment between the mark and the spindle pole would shorten due to depolymerization at the pole. The segment between the mark and the kinetochore would remain the same length because depolymerization is not occurring at the kinetochore end in this hypothetical scenario.