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Lecture21_slides_17Oct11

Lecture21_slides_17Oct11 - Selection Evolution is any...

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10/17/2011 1 Genetic change may occur through: • Natural Selection • Genetic Drift A genetic definition of evolution: Evolution is any genetic change in a population. • Migration Mutation 1. There must be phenotypic variation in the population, and that phenotypic variation has Selection … happens when individuals vary in fitness, due to some having higher rates of survival and/or reproduction. to affect fitness . 2. The phenotypic variation that affects fitness must be inherited from parent to offspring. (Non-genetic phenotypic variation does not contribute to evolution.) Definition of FITNESS (of a genotype) Selection … happens when individuals vary in fitness, due to some having higher rates of survival and/or reproduction. The average genetic contribution of individuals of that genotype make to the next generation. This means fitness is strictly a function of reproductive success! However, you have to survive to reproduce, so survival (of the fittest) also matters. Definition of FITNESS (of a genotype) The average genetic contribution of individuals of that genotype make to the next generation. In real life, we can never experimentally measure “fitness”. The best we can do is estimate it based on phenotypes we think are good predictors of fitness. For example: • survival mating success number of progeny produced Two common modes of natural selection: 1. Purifying selection testing for purifying selection mutation-selection balance 2 Di ti l l ti Ways in which selection can act on phenotypes , regardless 2. Directional selection genetically simple directional selection testing for directional selection of the underlying genetic basis. opulation ection Purifying (stabilizing) selection Orange arrows indicate phenotypes disfavored by selection. phenotypic value frequency in p before sele
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