Figure 2

Example of unicity score computing for a gene tree with two different rootings. In this tree, we have six sequences a₁, a₂, b₁, b₂, b₃ and c. Sequences a₁ and a₂ belong to species A; b₁, b₂ and b₃ belong to species B; and c belongs to species C. Scores of internal nodes are given in the circles. In this example, the rooting for topology (A) gives the unicity score U^(T)= ln(6)+ ln(6)+ ln(4)+ ln(2)+ ln(1)≈5.663, and the rooting for topology (B) gives the score U^(T)= ln(6)+ ln(4)+ ln(1)+ ln(1)+ ln(1)≈3.178. The rooting in (B) is therefore preferred over the one in (A).