Final answer:
Chromosome segregation is not a transition point where the cell cycle control system regulates progression, as it is part of mitosis rather than a specific regulated checkpoint like G1/S, G2/M, or metaphase checkpoints.
Step-by-step explanation:
The question is asking which event is not a transition point where the cell cycle control system regulates progression through the cell cycle. The three major checkpoints are at the end of G1 (G1/S transition), at the G2/M transition, and during metaphase.
These checkpoints ensure the integrity of DNA, proper chromosome duplication, and correct attachment of kinetochores to spindle fibers, respectively. Since chromosome segregation occurs later in the cell cycle during actual mitosis and not at a specific control transition point, it is not one of the regulated transitions in question. Therefore, chromosome segregation is not a transition point where the cell cycle control system regulates progression.