FIGURE 6.

On a coarse-grained level, the dynamics of mutation opening/closing can be described by a model of two particles hopping on a one-dimensional lattice, with inward/outward hopping rates k_in, k_out. Their positions represent the two outermost closed mutations. When the particles collide, all mutations have opened. Equivalently, one can consider a single particle hopping on a triangular two-dimensional lattice. The first collision time then corresponds to the time to reach the diagonal absorbing boundary.