Lec21_Drift - BioG1780 Evolution and Biodiversity Lectures...

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BioG1780 Fall 2010 Evolution and Biodiversity Today’s lecturer: Matt Hare Lectures 21: Oct 18, 2010 GENETIC DRIFT Reading: Ch. 7, section 2 This lecture is the fourth in a series on microevolution. In previous lectures we defined the baseline against which we will measure genetic change (Hardy-Weinberg Equilibrium) and examined mutation and selection as mechanisms of allele frequency change. Today we will examine several more examples of how selection makes directed change in allele frequencies, and then we will turn to the undirected (random) changes caused by genetic drift. A. Populations are not infinite in size (as assumed in HWE). 1. Chance events that affect adults can change allele frequencies in a population; this is genetic drift. 2. Random sampling of gametes to form a finite-sized zygotic generation can change allele frequencies from one generation to the next; this is also genetic drift and a more pervasive mechanism by which chance changes allele frequences. 3. Genetic drift is evolution, but it is a random process producing random allele frequency change, not adaptive change.
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