This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Retinoblastoma gene regulates- 
Select and explain. 
A. Gi - S phase, B. G2 - M phase, C. Go - S1 phase, D. S - G1 phase
A: Gi - S phase
Answer: A: Gi - S phase 
Explanation: Ans. is 'a' i.e., G1- S phaseo Phosphorylation of RB is a molecular "On-off' switch for cell cycle.o It regulates cell cycle at G,- S phase (has been explained in details in previous explanations).