Since this multiple change would only appear to be

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Unformatted text preview: ino acid has changed more than once. Since this multiple change would only appear to be one substitution, it is necessary to compensate using the following formula: ! raw substitutions # Corrected substitutions = - 100ln 1 " $ 100 in this case : ! 33 # corrected sub' s = - 100ln 1 " 100 $ = - 100ln(0.67) = 40 corrected substitutions With fewer than 10 substitutions, the correction is not necessary. For cytochrome c, one substitution occurs roughly every 21 million years. Therefore humans and plants last common ancestor lived about 850 million years ago. This agrees roughly with the fossil record. Graph from The Structure and Function of Proteins Dickerson & Geis. Corrected # of amino acid substitutions Evolution 9 - 3 Molecular phylogeny & criminal justice • • • • 1994: Dr. Richard Schmidt accused of injecting his ex-girlfriend (the Victim) with HIV (AIDS virus) from one of his patients. HIV evolves very rapidly, even leading to multiple different sequences in the same patient! Police collected HIV samples from victim (V), Dr. Schmidt’s patient (P), and many local HIV+ individuals from the community who were unrelated to the case (LA) They then used computer tools to construct the following phylogeny. From: “Molecular evidence of HIV-1 transmission in a criminal case” by Michael L. Metzker, David P. Mindell, Xiao-Mei Liu, Roger G. Ptak, Richard A. Gibbs, and David M. Hillis. Proceedings of the National Academy of Sciences 99:22 14292-14297 (2002). Evolution 9 - 4...
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