BILD 3 Lecture Notes - Lecture 13: Paraphyly, Polytomy, Branch Point
30 May 2016
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Lecture 13 4/25/16: how to read a phylogenetic tree. Node (branch point): re presents the common ancestor of lineages (>2 branches from one node is a polytomy) Species or taxa (single: taxon): twig tips (end points generally) Share an immediate common ancestor and are each other"s closest relatives. Branch length: may or may not be informative. Unless there is explicit information telling you what branch length means, assume it"s nothing. Branch lengths can be scaled to the fossil record but generally isn"t. Most trees are rooted to an unlabeled branch that corresponds to the common ancestor for all of the species in the tree: a phylogenetic tree is a hypothesis about how evolution happened. As a result, phylogenetic trees are made of clades. A group of taxa and their most recent common ancestors. That is: an ancestor (node) and everything that is descendant of it is a clade: categories of taxonomic groupings.
