BIO 201 Lecture Notes - Lecture 15: Phylogenetics

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22 Mar 2018
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Outgroups are central to determining character polarity (the direction of evolutionary change). Outgroups serve as a reference point, and inform us of the directionality of character evolution. We use the outgroup to help us determine which hypothesis of change (a, b, or c) is most likely. Number of taxa determines the number of possible phylogenies for a set of taxa. The number of taxa in a data matrix determines the number of phylogenies (hypotheses) that need to be evaluated. The data (characters and states) are used to find which of these phylogenies is best supported. Example: 3 taxa = 3 possible relationships. Parsimony is used to determine which hypothesis is best. Parsi(cid:373)o(cid:374)(cid:455) (cid:373)a(cid:455) (cid:271)e defi(cid:374)ed as (cid:862)the (cid:271)est solutio(cid:374) gi(cid:448)e(cid:374) the data that (cid:449)e ha(cid:448)e(cid:863) or (cid:862)the simplest solutio(cid:374) is the (cid:271)est solutio(cid:374). (cid:863) Parsimony is a central philosophical principle of all the sciences; it is not unique to phylogenetics.

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