lecture17 - BioEE 278 Evolutionary Biology Spring 2007...

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BioEE 278 Spring 2007 Evolutionary Biology Lecture 17 GENETIC DRIFT & GENE FLOW Reading: Ch. 10, pp. 225-235; Ch. 12, pp. 278-280 (section on “Selection and gene flow”) A. Genetic drift and chance events in evolution of populations 1. Chance in the transmission of alleles from one generation to the next. a. populations aren’t infinite (as in H-W); b. a single family: the ratio of alleles in offspring may not reflect exactly the ratio of alleles in parents. c. the same applies to small populations (small collections of mating pairs), even if mating is random. d. genetic drift: deviations from expected allele frequencies (under H-W) due to chance events – in who mates or what some gametes are transmitted to the next generation. e. abandon deterministic view - that we can clearly predict p t+1 from p t f. adopt a more probabilistic view - that there is a distribution of p t+1 given some value of p t B. Single-locus Models of Genetic Drift 1. Outcome of genetic drift. a. although changes in allele frequency due to random drift cannot be predicted,
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lecture17 - BioEE 278 Evolutionary Biology Spring 2007...

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