Bio Outline 3

Bio Outline 3 - Processes of Evolution Class Discussion In...

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Processes of Evolution Class Discussion In 17 th , 18 th century Europe—almost everyone believed in Creationism and that the earth was 6,000 years old (which was worked out as an estimate by Archbishop James Ussher in 1650). I. Natural Selection (NS) “Descent with modification” A. Key observations by Darwin: 1. Species tend to: over-reproduce 2. Individuals in a population: vary extensively 3. These varying traits: are inherited B. Conclusion – the varied traits that an individual inherits affects this individual’s ability to: secure limited resources to better survive and reproduce Traits that are “better” than others for a particular environment become: more prevalent— microevolution —change in allele frequency in a population over time C. Natural Selection (NS) = differential reproductive success. In other words, individuals whose characteristics best adapt them to their CURRENT environment are most likely to survive and reproduce. Successful or “fit” individual = well adapted to their environment to pass along their genes D. Three key points about NS 1. NS is an editing process, not a creative process. What does this REALLY mean? 2. NS is contingent on: time and place (environment is unstable) 3. Significant evolutionary change can occur in a short time. 1
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II. Population Genetics Charles Darwin – in 1859, published theory of NS , without knowing about inherited traits/genes ( Gregor Mendel – 1860’s his work was not recognized until 40 years after the Origin of Species was published). Darwin, therefore, did not understand WHERE the variation of individuals came from. Interestingly, Darwin’s theory was attacked because of the lack of understanding of genes—it was argued that if two animals were blended (like horse and zebra) traits would be diluted and offspring would never have clear advantages.) Darwin was so unsure that he even stopped arguing his theory! A. = Modern synthesis (1940’s) - The ideas of Darwin and Mendel together. How is it different from Darwin’s theory of NS? 1. It recognizes 4 processes of evolution, not just natural selection -gene flow -genetic drift -mutation 2. It recognizes that “traits” = genes (2 alleles) B. NS acts on individuals but the effect is a change in the population . C. population : group of organisms of the same species living at the same time/place D. Microevolution – change in allele frequency in a population over time III. Hardy-Weinberg model of a non-evolving population (a.k.a non-evolution) A. Do non-evolving populations exist? NO—this is a theoretical model What 5 conditions would have to be met? For non-evolution to be true Mutations? No Size? Infinitely large Immigration/Emigration? No—isolated population Mating? Random Reproductive success? Equal among all—same number of offspring B. Hardy-Weinberg Principle (1908): if these five conditions are met, there is no evolution *Sexual reproduction alone does not lead to evolution* 2
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Butterfly example: an imaginary butterfly population is in genetic equilibrium (a.k.a. “Hardy-Weinberg
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This note was uploaded on 10/10/2011 for the course BIOL 101 taught by Professor Hogan during the Fall '08 term at UNC.

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Bio Outline 3 - Processes of Evolution Class Discussion In...

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