This preview shows pages 1–3. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.View Full Document
Unformatted text preview: 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 ction Purifying (stabilizing) selection Orange arrows indicate phenotypes disfavored by selection. phenotypic value phenotypic value frequency in p before sel e 10/17/2011 2 opulation ction Purifying (stabilizing) selection phenotypic value frequency in p after sele c Purifying (stabilizing) selection Most fit ( evolutionarily ) Strong purifying selection can cause a departure from Hardy-Weinberg Equilibrium. HWE is our null hypothesis: • no mutation • infinite population size • no selection • no migration • random mating If the real data are not compatible with HWE, we reject the null hypothesis and conclude (at least) one of the HWE assumptions has been violated. Strong purifying selection cause a departure from Hardy-Weinberg Equilibrium. Jaeken syndrome: deficiency of glycoprotein synthesis due to mutation in phosphomannomutase gene PPM2 http://www cdgs com/popupbasic html http://www.cdgs.com/popupbasic.html Strong purifying selection cause a departure from Hardy-Weinberg Equilibrium....
View Full Document
This note was uploaded on 01/01/2012 for the course BIOEE 1780 taught by Professor Harrison during the Fall '10 term at Cornell University (Engineering School).
- Fall '10