Final answer:
The correct answer is A) G1 Checkpoint, which ensures that the cell is ready with proper size, energy reserves, and intact DNA before entering the S phase.
Step-by-step explanation:
The question is asking what is maintained by inactivating S- and M-Cdks after the M phase. The inactivation of these cyclin-dependent kinases is crucial for ensuring that the cell cycle progresses in an orderly manner. The correct answer to this question is A) G1 Checkpoint. The G1 Checkpoint is responsible for assessing whether the cell has the appropriate size, energy reserves, and undamaged DNA before proceeding into the S phase, where DNA replication occurs. By inactivating S- and M-Cdks after M phase, the cell ensures that it does not prematurely re-enter S phase without first completing necessary preparations in G1.
The M checkpoint occurs near the end of the metaphase stage of karyokinesis. The M checkpoint is also known as the spindle checkpoint, because it determines whether all the sister chromatids are correctly attached to the spindle microtubules. Because the separation of the sister chromatids during anaphase is an irreversible step, the cycle will not proceed until the kinetochores of each pair of sister chromatids are firmly anchored to at least two spindle fibers arising from opposite poles of the cell.