Figure 2.

Illustration of dynamical processes changing the PID histogram. (panel A) The PID decay generates a negative flux v(p)N_a(p) down the PID-axis. The net flux into a given bin Δp is given by v(p + Δp)N_a(p + Δp) - v(p)N_a(p) ≈ $\Delta p\frac{d}{dp}[v(p)N_a(p)]$ (panel B) A single gene duplication event A → A' gives rise to three new paralogous pairs: A' - A, A' - B and A' - C. Immediately after the duplication the pair A - A' has the PID = 100%, while PIDs of A' - B and A' - C are equal to those of A - B and A - C. Thus the PID of every previously existing paralogous pair involving A gets duplicated along with the duplication A → A'.