Figure 3 .
(A) A two-state Markov model for ancestry along a chromosome for a single pulse of migration at time t1. Tract-length distributions are exponential. (B) A three-population Markov model with a pulse of blue and red ancestry at time t1 followed by a pulse of migration from the yellow population at time t2. All tract-length distributions are exponential. (C) A two-population model in which the blue population contributes migrants at generation t1 and t2. The distribution of blue ancestry tracts is no longer exponential, as we cannot detect transitions between blue states.