Final answer:
The three cell cycle checkpoints are located near the end of G1, at the G2/M transition, and during metaphase. They evaluate the DNA integrity, proper chromosome duplication, and kinetochore attachment to spindle fibers, respectively.
Step-by-step explanation:
The three cell cycle checkpoints are critical for ensuring the proper division and replication of cells. The first checkpoint occurs near the end of the G1 phase, where the integrity of the DNA is assessed. If the DNA is damaged, repair mechanisms are activated, or the cell is directed to apoptosis to prevent further propagation of errors. As the cell prepares to enter mitosis, the second checkpoint at the G2/M transition evaluates the proper chromosome duplication. This ensures that each sister chromatid is an accurate copy of the original chromosome. Finally, during the metaphase stage, proper attachment of each kinetochore to a spindle fiber is checked during the M checkpoint to ensure correct chromosome alignment and segregation.