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The tree produced is a - autapomorphies which will not be...

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The tree produced is a Phenogram and is one way to infer relationships. Why might this tree not reflect phylogeny (true ancestor descendant relationships)? 1) Variable evolutionary rates : faster evolving taxon will be more different from all others and appear as an "outgroup" 2) Homoplasy (convergence) will tend to make character states similar between unrelated taxa and the UPGMA approach will join them. Cladistics : classification reflects sequence of branching events, not degree of difference/similarity. See figures 17.6 and 17.7, pages 471-472. Classification is on shared derived characters (synapomorphies) . Note that relationships are never based on the absence of characters (e.g., "Invertebrates" makes sense to us, but refrigerators and pizzas are "invertebrates" because they don't have back bones, but they clearly are not related to animals. For that matter, plants are invertebrates!). Tree produced is a Cladogram and is a hypothesis of relationship . A taxon can evolve at a different rate, but it will tend to accumulate
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Unformatted text preview: autapomorphies which will not be shared with any other taxa and thus will affect the branch pattern less (but variable rate can lead to incorrect cladograms). How about Homoplasies ? They will affect the hypothesis since those characters showing convergences (or parallelisms) will contradict data from other characters. This brings us to the topic of Parsimony : in constructing cladograms we seek that branching pattern which requires the fewest number of evolutionary steps . Example of marine mammals (chosen since we know that it is an example of a convergence). It is more parsimonious to evolve fins twice and all the characters that hold mammals together once, than it is to evolve fins once and all the characters that ally whales with other mammals twice. We tolerate fins as Homoplasies (=analogies) since it is much more parsimonious than calling all the mammalian characters homoplasies. See fig. 17.13, pg. 485 and work through it....
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