BioG1780 Fall 2010 Evolution and Biodiversity Today’s lecturer: Matt Hare Lecture 23: Oct 22, 2010 Natural Selection on Quantitative Traits READING: Chapter 9, all sections except 2 A. Quantitative traits 1. Traits exhibiting continuous phenotypic distributions • normal (bell shaped) distribution, mean, variance 2. Traits determined by many independent loci 3. Traits influenced by the environment B. Selection on quantitative traits 1. Directional selection • shifts mean, reduces variance 2. Stabilizing selection • mean doesn’t change, reduces variance 3. Disruptive selection • mean doesn’t change, variance increases C. Heritability 1. Phenotypic variance has genetic and environmental components; V P = V G + V E a. genetic variance in populations has additive and dominance components; V G = V A + V D b. V A is genetic variation among individuals stemming from simple additive allele effects c. V D is genetic variation among individuals from gene interactions such as dominance
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