Bio 201 F08 True lect 6v2r

Bio 201 F08 True lect 6v2r - Recall from last lecture...

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Recall from last lecture • Synonymous nucleotide substitution – Does not change the animo acid coded for – e.g. CGC (arginine) -> CGA (arginine) • Nonsynonymous substitution – Changes the animo acid coded for – e.g. C GC (arginine) -> A GC (serine)
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Selection at the molecular level Recall two types of selection from a previous lecture – Positive (directional) and stabilizing Neutral evolution – Rate of synonymous substitution approx. = rate of nonsynonymous substitution Stabilizing selection (selection for no change) – Rate of synonymous substitution > rate of nonsynonymous substitution Positive (directional) selection (selection promotes change in amino acid sequence) – Rate of synonymous substitution << rate of nonsynonymous substitution
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Evolution of foregut fermentation Posterior esophagous or stomach modified to hold bacteria, which digest plant matter (cellulose) via fermentation Evolved independently in primates (langurs) and ruminants (cattle) Also evolved independently in one lineage of birds ( hoatzin)
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Molecular evolution of lysozyme in foregut fermenters Most animals, defensive enzyme (digests bacterial cell walls) In foregut fermenters, modifications of lysozyme have evolved Enables some foregut bacteria to release nutrients, which are absorbed as food 5 amino acid changes have evolved independently in both langurs and cattle Some of these have also evolved in hoatzins
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• Why? – Complexity
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This note was uploaded on 04/14/2009 for the course BIO 201 taught by Professor True during the Fall '08 term at SUNY Stony Brook.

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Bio 201 F08 True lect 6v2r - Recall from last lecture...

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