Phylogenetic test of the molecular clock and linearized trees

To estimate approximate divergence times of species or species groups withmolecular data, we have developed a method of constructing a linearizedtree under the assumption of a molecular clock. We present two tests of themolecular clock for a given topology: two-cluster test and branch-lengthtest. The two-cluster test examines the hypothesis of the molecular clockfor the two lineages created by an interior node of the tree, whereas thebranch-length test examines the deviation of the branch length between thetree root and a tip from the average length. Sequences evolving excessivelyfast or slow at a high significance level may be eliminated. A linearizedtree will then be constructed for a given topology for the remainingsequences under the assumption of rate constancy. We have used thesemethods to analyze hominoid mitochondrial DNA and drosophilid Adh genesequences.