<prompt> Retinoblastoma gene regulates-Gi - S phaseG2 - M phaseGo - S1 phaseS - G1 phase  <response>: 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. 