BB lecture 2-6-09, population evolution

BB lecture 2-6-09, population evolution - Chapter 23 -...

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Unformatted text preview: Chapter 23 - continued (pp.476-484) Population evolution Learning objectives: • Differentiate between gene flow and genetic drift • Know examples of directional, disruptive, and stabilizing modes of selection • Explain how heterozygote advantage and frequency-dependent selection promote balanced polymorphism • Explain why natural selection does not produce perfect organisms Quiz 3: Practice ‘collaboration’ Review… – Natural selection – Genetic drift – Gene flow… • These are the major factors that alter allele frequencies and bring about most evolutionary change The Founder Effect – another type of genetic drift • The founder effect – Occurs when a few individuals become isolated from a larger population • Inbreeding – Breeding of closely related individuals – Can cause allele frequencies in the new population to differ from the original population Genetic drift Effects of Genetic Drift : A Summary 1. Genetic drift causes allele frequencies to change at random 1. Genetic drift is most pronounced in small populations 1. Genetic drift can lead to a loss of genetic variation within populations 1. Genetic drift can allow harmful alleles to become fixed (only one allele exists in the population) Gene Flow …due to immigration & emigration (but not migration…why?) • Gene flow – Causes a population to gain or lose alleles – Results from the movement of fertile individuals or gametes, helps maintain a level of genetic diversity – Tends to reduce differences between populations over time Fig. 23-12 NON- MINE SOIL MINE...
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This note was uploaded on 02/26/2009 for the course BIO 311D taught by Professor Reichler during the Spring '08 term at University of Texas.

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BB lecture 2-6-09, population evolution - Chapter 23 -...

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