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Figure 2 | BMC Evolutionary Biology

Figure 2

From: Utility of characters evolving at diverse rates of evolution to resolve quartet trees with unequal branch lengths: analytical predictions of long-branch effects

Figure 2

Two classic quartet branch length conditions in which long-branch effects can arise. A) Four-taxon tree modeled by Huelsenbeck and Hillis [22]. The internode and two subtending branches labeled a are constrained to have the same length (i.e. “three-branch length”), so are the two subtending branches labeled b (i.e. “two-branch length”); p a and p b represent the three-branch length and two-branch length (evaluated via Equation 9), respectively. B) Alternative four-taxon tree modeled by Siddall [26]. The internode and two subtending branches labeled a’ are constrained to be equal in length (i.e. “alternative three-branch length”), so are the two subtending branches labeled b’ (i.e. “alternative two-branch length”), with p a and p b representing the alternative three-branch length and two-branch length, respectively. C) Branch length space of the model tree investigated by Huelsenbeck and Hillis [22], with the three-branch length p a on the horizontal axis and the two-branch length p b on the vertical axis. These axes apply to Figures 3A, C, and E. The upper-left portion of this branch length space corresponds to the Felsenstein zone. D) Branch length space of the alternative model tree investigated by Siddall [26], with the alternative three-branch length p a on the horizontal axis and the alternative two-branch length p b on the vertical axis. These axes correspond to those in Figures 3B, D, and F. The upper-left portion of this branch length space corresponds to the Farris zone as termed by Siddall [26].

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