Temporal evolution of variables related to the first hazard in the budding yeast cell cycle model. X-axis and y-axis represent the time and the level of activation concentration in simulation, respectively. (A) The low level activation of Clb2 through the time of 30 to 45 causes the transcription of Mcm1. Finally, Clb2 is activated to a high level by Mcm1. (B)-(C) At the time of 5, both Clb2 and Mcm1 are activated and do not form a positive feedback. (D) Clb2 is first activated at the time of 4, and then Mcm1 is activated. After the transcription of Mcm1, Clb2 is activated to value of 2, a high activation level, at the time of 7.