lecture18 - BioES 278 Evolutionary Biology SELECTION ON...

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BioES 278 Fall 2007 Evolutionary Biology Lecture 18 SELECTION ON GENES AND PROTEINS Reading: Ch. 10, pp. 235-240 A. Patterns of variation and divergence at the DNA sequence level. 1. How do DNA sequences (and the proteins they encode) evolve? a. what evolutionary forces shape variation and divergence in DNA sequences? b. what role for selection and drift? 2. Gene structure. a. most eukaryotic genes consist of transcribed region flanked by 3' and 5' non- transcribed regions. b. non-transcribed regions may contain regulatory elements. c. transcribed regions consist of coding regions ( exons ) interrupted by non-coding sequences ( introns ). 3. Genetic code. a. nucleotides and pairing: purines (A,G) and pyramidines (C,T); A pairs with T, G with C. b. Mutation rates: transitions > transversions. c. triplet, degenerate code. d. can characterize nucleotide sites as non-degenerate (any substitution results in a.a. change), two-fold degenerate (transversions cause a.a. change, but transitions dont), four-fold degenerate (base substitution never causes change) e. can characterize substitutions as non-synonymous (replacement) and synonymou s (silent). f. all 2
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lecture18 - BioES 278 Evolutionary Biology SELECTION ON...

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