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. Author manuscript; available in PMC: 2014 Dec 1.
Published in final edited form as: Trends Ecol Evol. 2013 Oct 1;28(12):10.1016/j.tree.2013.09.004. doi: 10.1016/j.tree.2013.09.004

Figure 3. Incomplete lineage sorting.

Figure 3

As the evolution of three sampled alleles (blue solid circles at the bottom) is traced backward in time, alleles from A and B might fail to coalesce in the ancestral population. This results in all three alleles entering the ancestral population of all three species, and the alleles from B and C coalescing first, by chance, giving rise to a gene tree that is incongruent with the species tree. The probability of this event happening in this scenario is a function of the branch length, t, as measured in coalescent units (one coalescent unit equals 2N generations, where N is the population size).