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Unformatted text preview: . Distinguishing between cladograms , phylograms and chronograms . BIS2C W2009 Lectures 2-3 (7 January 2009) 2 How do we reconstruct phylogenetic trees? Trees are inferred from the similarities that are observed among taxa. Trees as hypotheses. Characters , character states , and coding of characters. Kinds of characters. Character-taxon data matrix . The principle of parsimony: searching for a tree that requires the fewest steps. What is an unrooted tree ? Basic procedure for finding/searching for the most parsimonious tree. 1. Ignore parsimony-uninformative characters. 2. Draw possible trees. 3. For each informative character count the minimum number of steps required on each tree. 4. Sum over all characters to get the score (number of steps) for each tree. 5. The most parsimonious tree(s) is/are the one(s) with lowest score. 6. Root the tree along the branch leading to the outgroup (if known). Example: four-taxon problem....
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- Winter '08