Figure 2.

GOC Procedure. (1) A gene tree G reconciled with species tree S. Duplication nodes are denoted by a black square. The leaves and internal nodes of G are labeled with the letter of their corresponding species. Brackets denote the required orthologs given by the input set P = {(a₁, b₂), (a₁, c₁), (a₁, c₂)}. The non-preservable nodes (nodes of H) are depicted by red crosses, while preservable nodes are circled in green. (2) The species tree associated with G. (3) The tree G_P, a solution to the GOC problem, which preserves every possible clade.