presentation_6_7 - Lecture 6 (contd) Phylogenetics I...

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Lecture 6 (cont’d) Phylogenetics I Phylogenetic analysis
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Synapomorphies synapomorphies are shared by subsets of species and are the characters that define the presumed history of descent. C 1 : sp. 1-3 f 1 , g 1 : sp. 2-3 Fig. 2.4 Symplesiomorphies Fig. 2.4 a 0 ,b 0 ,c 0 ,d 0 ,e 0 ,f 0 ,g 0 ,h 0 ,I 0 ,j: symplesiomorphy for group of all species. C 1 : symplesiomorphy, group of sp. 2-3 C 1 : synapomorphy, group of sp. 1-2
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autapomorphies are not shared by species and do not contribute to our understanding of relationships Autapomorphies Fig. 2.4 autapomorphies can lead to incorrect inferences if we rely on overall similarity species 1 and 3 are the “most similar” - many changes along the branch leading to species 2 Autapomorphies can be a problem when rates of evolution vary Fig. 2.4
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Chimpanzee Gorilla Orangutan Human Relatives Family Hominidae (Great Apes and Humans) Gibbon Orangutan Chimp Gorilla Human
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examples of homoplasy - convergent or parallel change and character state reversal a typo! should be 1 Homoplasies Fig. 2.4 Phylogenetic inference Infer phylogenetic history - construct a tree that reflects history and pattern of descent (not necessarily overall similarity). Ignore autapomorphies; try not to be fooled by homoplasy; distinguish symplesiomorphies from synapomorphies. Inferred tree or cladogram is a hypothesis of the origin of derived character states. • But… How do we know what’s ancestral & what’s derived?
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Defining character polarity • How do we identify which character states are ancestral and which are derived?
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This note was uploaded on 09/28/2008 for the course BIOEE 2780 taught by Professor Geber during the Fall '07 term at Cornell University (Engineering School).

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presentation_6_7 - Lecture 6 (contd) Phylogenetics I...

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