lecture16F06

lecture16F06 - Lecture 16: Natural selection Assigned...

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Lecture 16: Natural selection Natural selection fitness; micro- vs. macroevolution Patterns of natural selection directional, balancing, stabilizing, disruptive, diversifying An examples of directional and balancing selection HIV drug resistance; influenza viral evolution; sickle-cell disease Sexual selection secondary sexual characteristics, intersexual, intrasexual selection Assigned Readings: Ch. 23 Guppies as an example of natural and sexual selection natural versus cultivated strains, field observations of effects of predators on male color, experiments on balance of natural and sexual selection, field experiments
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Anytime there is unequal survival and/or unequal reproduction of genotypes, there is selection . Fundamentally, it results in changes in the frequencies of alleles. Fitness = a quantitative measure of an individual organisms ability to survive and reproduce. Natural selection - what it is
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The existence of natural selection is not doubted by anyone, even including most of those with creationist beliefs. Natural selection, together with random mating, genetic drift, mutation, and other forces, explains microevolution with substantial accuracy. The controversy is over whether natural selection is adequate to explain macroevolution, or large-scale differences between species. Natural selection - what the controversy is about
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There are 3 basic patterns of natural selection (same 3 occur with artificial selection also): They are basically the same whether one is studying selection on discrete characters - e.g., white flowers vs purple flowers or quantitative characters - (polygenic or multifactorial characters) - e.g., height, weight, etc.
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fitness Balancing or stabilizing selection: Aa has higher fitness than AA and aa Outcome : alleles A and B can be maintained (not fixed by drift) AA Aa aa Directional selection: AA Aa aa Diversifying or disruptive selection: Aa has a lower fitness than AA and aa Outcome : alleles A and B can be maintained (not fixed by drift) under s pecial conditions. AA Aa aa AA has higher fitness than Aa and aa Outcome : allele A replaces a Selection on discrete traits
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Balancing or stabilizing selection: Aa has higher fitness than AA and aa Outcome : alleles A and B can be maintained (not fixed by drift) AA Aa aa Directional selection: AA Aa aa Diversifying or disruptive selection: Aa has a lower fitness than AA and aa Outcome : alleles A and B can be maintained (not fixed by drift) under s pecial conditions. AA
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lecture16F06 - Lecture 16: Natural selection Assigned...

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