Probability that genes are in the active state (A), the mean number of proteins of each type present in the cell 〈n(i)〉(B), and the mean number of proteins of each type present in the cell if gene i is in the on-state 〈n1(i)〉 (C) as a function of Xad = δXsw for a symmetric switch. Exact solutions of the SCPF approximation equations compared with deterministic kinetic rate equations solutions, for a single symmetric switch, Xeq = 1000, ω = 0.5.