Lecture 17 figs

# Lecture 17 figs - v i v j v i v j Note the reason for...

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General Method (Felsentstein Fig. 9): Note that branch lengths are proportional to time , i.e., an evolutionary clock is assumed. 1. Find two tips on the phylogeny that are adjacent, say i and j and have a common ancestor k . 2. Compute the "contrast" X i -X j (note: " X " represents the character of interest, e.g., body mass). The contrast has expectation 0 and variance proportional to v i + v j . 3. Remove the two tips from the tree; node k is now a tip. Assign it character value X k = [(1/ v i ) X i + (1/ v j ) X j ] / (1/ v i )+(1/ v j ) 4. Lengthen the branch below node k by increasing its length from v k to v k +

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Unformatted text preview: v i v j /( v i + v j ). * Note: the reason for increasing the branch length below node k is that step 3 estimates the character state of node k with error equivalent to an additional amount of evolution after node k . 5. Repeat steps 1-4 until only one tip left on the tree. There will be n-1 contrasts for an n taxon tree. 6. Divide each contrast by the square-root of the variance (std. dev) to standardize the variance. This standardization is the means by which the contrasts are "moved" to the origin in the previous example (F&H fig. 9.13)....
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Lecture 17 figs - v i v j v i v j Note the reason for...

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