[Campbell Biology P.294] If the progression of cell cycle phases did not depend on cytoplasm... | Practice Question

If the progression of cell cycle phases did not depend on cytoplasmic molecules and each phase began only when the previous one was complete, how would the results of the cell fusion experiments Figure 12.14 have differed?

  • A: The G1 nucleus in both experiments would still immediately enter S phase or mitosis, demonstrating the dominance of the fused cell's state.
  • B: The G1 nucleus in both experiments would remain in G1 phase and not progress until its own internal conditions were met for S or M phase, respectively.
  • C: The S phase nucleus would be forced back into G1 phase by the G1 nucleus, indicating G1 dominance.
  • D: Only Experiment 1's results would differ, as S phase is less dependent on cytoplasmic signals than M phase.

Explanation

The original experiments showed that cytoplasmic molecules from S or M phase could force a G1 nucleus to enter those phases prematurely. If progression did not depend on cytoplasmic molecules, and each phase only began after the previous one was complete i.e., regulated by its own internal state , then the G1 nucleus would not be influenced by the fused cell's cytoplasm. It would remain in G1 until its own internal conditions were met, making it unable to prematurely enter S or M phase.