title: Counting phylogenetic invariants in some simple cases.
abstract: An informal degrees of freedom argument is used to count the number of phylogenetic invariants in cases where we have three or four species and can assume a Jukes-Cantor model of base substitution with or without a molecular clock. A number of simple cases are treated and in each the number of invariants can be found. Two new classes of invariants are found: non-phylogenetic cubic invariants testing independence of evolutionary events in different lineages, and linear phylogenetic invariants which occur when there is a molecular clock. Most of the linear invariants found by Cavender (1989, Molec. Biol. Evol. 6, 301-316) turn out in the Jukes-Cantor case to be simple tests of symmetry of the substitution model, and not phylogenetic invariants.
authors.affiliation: Department of Genetics, University of Washington, Seattle 98195.
authors.forename: J
authors.initials: J
authors.lastname: Felsenstein
mesh_terms: D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D008433:Mathematics; D008957:Models, Genetic; D010802:Phylogeny