PATHOLOGY

Detailed explanation-1: -The G 1start subscript, 1, end subscript checkpoint is the main decision point for a cell – that is, the primary point at which it must choose whether or not to divide. Once the cell passes the G 1start subscript, 1, end subscript checkpoint and enters S phase, it becomes irreversibly committed to division.

Detailed explanation-2: -The G1 checkpoint, also known as the restriction point in mammalian cells and the start point in yeast, is the point at which the cell becomes committed to entering the cell cycle.

Detailed explanation-3: -G2/M checkpoints include the checks for damaged DNA, unreplicated DNA, and checks that ensure that the genome is replicated once and only once per cell cycle. If cells pass these checkpoints, they follow normal transition to the M phase.

Detailed explanation-4: -The point at G1 at which commitment occurs and the cell no longer requires growth factors to complete the cell cycle has been termed the restriction (R) point. The R point has been temporally mapped at 2–3 hours prior to the onset of DNA synthesis.