AP BIOLOGY

Detailed explanation-1: -A checkpoint in the cell cycle is a critical control point where stoop and go-ahead signals can regulate the cycle. Animal cells generally have built-in stop signals that half the cell cycle at checkpoints until overridden by go-ahead signals.

Detailed explanation-2: -The main cell cycle checkpoints are the G1/S checkpoint, the intra-S checkpoint, and the G2/M checkpoint [60]. The transition through stages of the cell cycle is regulated by the action of cyclin-dependent kinases, which are key targets for modulations induced by different cellular stimuli, including DNA damage.