BIS2C_Lect2_Ward_Tree_Concepts_ppt

BIS2C_Lect2_Ward_Tree_Concepts_ppt - BIS2C Winter 2012(Ward...

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1 BIS2C Winter 2012 (Ward) Lecture 2. Fun with trees (cont d) Today s second lecture (9 Jan) more tree terminology and concepts phylogeny and classification Wednesday (11 Jan) methods for building trees terminal taxa u v x y z root, root node internal nodes internal branches w Internal nodes represent hypothetical ancestral taxa t So far we have been discussing bifurcating trees. These are trees in which each internal node gives rise to two descendant branches. Sometimes we draw trees in which some nodes have three or more descendant branches. Such nodes are called polytomies and they usually reflect uncertainty about phylogenetic relationships. polytomy An extreme case of ignorance: a completely unresolved bush polytomy
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