An oscillator cell cycle model needs no first or second chance event.

Abstract

Theoretical data is presented to support the view that a limit cycle oscillator model of the cell cycle (as originally described) which accounts for random triggering of replication, can also accommodate the experimental results which have caused the supporters of the Transition Probability model to introduce the occurrence of yet a second chance event. In particular, it explains why the addition of a suboptimal amount of mitogen in a split dose alters the probability of triggering at each treatment but, generally, has little effect on the delay before the initiation of S-phase. It is also confirmed that, other than in some exceptional circumstances, lowering the probability of triggering in the oscillator model may have little effect on the minimum "intermitotic" time (as required by the evidence of the Transition Probability proponents) and, moreover, the oscillator concept provides reason why this should be so.