Parsimony is central to the cladistic method and can be used for both studying the Polarity (direction of evolution in a transformation series ) of characters and the confidence of hypotheses of relationships. Example: Drosophila chromosome banding patterns (e.g., chromosomal inversions, figs. 17.16 and 17.17, pg. 491, 494). Each species has a distinct pattern of bands in their salivary gland chromosomes. The sequence of bands appears to have been inverted for certain sections of the chromosome during evolution. One can determine a network of likely evolutionary steps from one species to another. Big problem: can start anywhere in the network. Need to establish where the network begins, i.e. where to Root the tree ? Choose an Outgroup : A taxon (or taxa) that are known to lie outside that group in question and are thus believed to be ancestral to the ingroup. Requires independent information . Once properly selected the determination of polarity falls out logically based on parsimony. the identification of an outgroup can help identify
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