This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General anatomy, Subject name: Anatomy
The tumor suppressor gene p 53 induces cell cycle arrest at 
Select and explain. 
A. G2_M phase, B. S_G2 phase, C. G2_Sphase, D. G0phase
C: G2_Sphase
Answer: C: G2_Sphase 
Explanation: Ref Robbins 8/e p290-291 ,9/e p294 The cell cycle has its own internal controls called checkpoint, there are two main checkpoints ,one at the G2/S transition and another at G2/M In the G1/S checkpoint ,cell cycle arrest is mostly mediated through p53, which induces the cell cycle inhibitor p21 Arrest of the cell cycle by the G2/M checkpoint involves both p53 dependant mechanism As can be deduced from above mentioned information that the p53 is associated with both the types of checkpoint , however G2 /M checkpoint can take place even without p53.hence option" C" is the preferred anwers