There are 3 Check points in the cell cycle.
1 G1 checkpoint.
2 G2 checkpoint.
3 Spindle checkpoint.
G1 checkpoint: It is the most essential part of the cell cycle and major step taking place in whether to divide or not. If the cell completes this phase and enters the S phase it becomes impossible to reverse the cycle and get back to the G1 step.
Once a cell passes this phase it will divide into 2 daughter cells, some of the things are required before a cell divides:
a) Nutrients
b) Proper DNA.
c) Enough size to divide.
G2 Checkpoint: Here the Damaged DNA will be checked and The process of DNA replication will complete here. For the damaged DNA is found, then the process of repairs will start for the DNA, and if detect any kind of problem the whole cycle will stop at the G2 phase.
If the cell can be repaired then it will go for repair, but if the cell DNA cannot be repaired it will go for Apoptosis or programmed cell death. By this cell will make sure that No damaged DNA will be passed further.
Spindle checkpoint/ M checkpoint: At this stage checks will be there for chromosome attachment to the spindle at the metaphase plate. At this stage, the cell checks that the sister chromatids are properly attached to the microtubules as it will become irreversible in anaphase. Sister chromatids should be firmly attached to the spindle fibers from the opposite poles at this stage.
At this stage all chromosomes should be aligned at the metaphasic plate, inability to do so will stop the whole process. Chromosomes should not be misplaced.