presentation_7_8 - Lecture 7(contd Phylogenetics II The...

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Lecture 7 (cont’d) Phylogenetics II The importance of DNA 1 0 1 1 1 3 1 1 1 1 0 2 0 0 1 0 1 1 0 0 0 0 0 O E D C B A 1. Look for changed states - 1 in sp. 1 & 2 - 1 & 1 in sp. 2 & 3 - 1 in sp. 1-3 - 1 in sp. 2 Pattern of character state changes to infer relationships. 2. Does a set of species more characters with state changes than others? synampomorphies group the set of species 3. Map other changes onto tree O 2 3 O 2 3 1 O 2 3 1
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Molecular clock: rate of sequence divergence between 2 taxa per unit time (Myr). Calibrate rates of sequence divergence by plotting amount of sequence divergence against time since lineage splitting. If this plot is linear, have a “molecular clock”. How old are divergence times? Molecular clocks Fig. 2.12 If rate of sequence evolution is ~constant the number of difference between a pair of taxa (e.g., B&A) should be proportional to the time since they diverged (split from a common ancestor).
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Fig. 2.12 Estimating divergence times from fossil data MRCA A B shares derived character states with A shares derived character states with B time
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Each point represents a pair of mammal species whose MRCA has been dated based on the fossil record. Time since MRCA (Myr) Fig. 2.13 Sequence divergence of the mitochondrial COI gene between pairs of vertebrate species Fig. 2.15
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Fig. 2.13
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