BIOL 125 Lecture Notes - Lecture 3: Petrified Wood, Astragalus, Polytomy
13 Jan 2017
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When adding taxa, can join taxa to any node of terminal branch. Algorithm that adds one taxa on at a time, starting from outgroup. Count # of steps between each group & outgroup. Start with group least amount of steps from outgroup, and continue in that order. When adding taxon to tree, least steps wins. If steps are equal, do most basal or determine alternate trees. After taxon added to tree, evaluate character states for nodes created. If polytomies, map characters onto tree and see if they can be resolved. Polytomies = more than 1 branch off of a node. If all else fails, adding more groups will give you a resolution (not more characters) Homoplasy - (same form) similar traits for reasons other than common ancestry (analogy) Convergent evolution - natural selection favours similar solutions to problems posed by similar ways of living. Selective pressures made my similar conditions favour evolution of similar solutions.
