Transc. X activates TFs Y1 and Y2. Y1 and Y2 activate each other. The input function at the Y1 and Y2 promoters is an OR-gate.

Transc. F. X activates TFs Y1 and Y2. Y1 and Y2 activate each other. The input function at the Y1 and Y2 promoters is an OR-gate. At time t=0, X begins to be produced from an initial concentration of X=0. All production rates are β=1 and degradation rates are α=1. All of the activation thresholds are K=0.5. At time t=3, X production stops.

(a) Plot the dynamics of X, Y1 and Y2. What happens to Y1 and Y2 after X decays away?