BioG1780 Fall 2010 Evolution and Biodiversity Today’s lecturer: Matt Hare Lectures 20: Oct 15, 2010 NATURAL SELECTION TEXT READING: Chapter 6, section 2 & 4 1. Selection occurs ONLY under the following conditions: a. Individuals vary in phenotype. b. Variation in phenotype results in variation in fitness. c. Variation in phenotype has a genetic basis. Note: Selection always acts at the phenotypic level, typically on traits that vary continuously and have a complex genetic basis (more on this in chapter 9, October 22). However, in this lecture we will examine how selection operates when trait variation has a simple genetic basis (e.g., single-gene diseases) because in these cases we can analyze selection on genotypes and see the influence of deleterious vs. adaptive mutations. 2. Fitness is defined as genetic contribution to future generations . a. Fitness is determined by genetics and the environment. b. Fitness can be measured in absolute terms.
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