PHYLOGENETIC TEST OF THE MOLECULAR CLOCK AND LINEARIZED TREES

To estimate approximate divergence times of species or species groups with molecular data, we have developed a method of constructing a line arized tree under the assumption of a molecular dock. We present two t ests of the molecular clock for a given topology: two-cluster test and branch-length test. The two-cluster test examines the hypothesis of t he molecular clock for the two lineages created by an interior node of the tree, whereas the branch-length test examines the deviation of th e branch length between the tree root and a tip from the average lengt h. Sequences evolving excessively fast or slow at a high significance level may be eliminated. A linearized tree will then be constructed fo r a given topology for the remaining sequences under the assumption of rate constancy. We have used these methods to analyze hominoid mitoch ondrial DNA and drosophilid Adh gene sequences.