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2011 SLIDE SET X Spr11

2011 SLIDE SET X Spr11 - SLIDE SET X V The Modern Synthesis...

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SLIDE SET X V. The Modern Synthesis: Population Genetics A. Darwin’s dilemma 1. Genetic variation in natural populations 2. Genes and mutation 3. The Hardy-Weinberg rule B. Populations and gene pools 1. Definitions 2. Illustration of Hardy-Weinberg equilibrium C. Conditions for Hardy-Weinberg equilibrium D. Significance of Hardy-Weinberg for the study of evolution E. How to recognize Hardy-Weinberg equilibrium
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VI . Forces that disrupt HW equilibrium A. Effects of chance in small populations - genetic drift 1. Bottlenecks 2. Founder effects B. Mutation C. Migration and gene flow D. Non -random mating E. Natural selection 1. a classic example: industrial melanism & the peppered moth SLIDE SET X (cont’d.)
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Darwin’s “dilemma” or the “paradox of evolution”: -Evolution requires variation , but natural selection eliminates variation variation in populations (recall: increase in frequency of “red” individuals over “blue”). -During Darwin’s day, “genes” were not known, and the cause of genetic variation (mutation) was not known. Post Darwin: -Rediscovery of Mendel’s work in the early 1900s (units of heredity) -Hugo de Vries (~1900): noted spontaneous appearance of NEW heritable variants in the evening primrose absent in true-breeding lines: called these “mutations” (source of novel hereditary variation) -1920s and 1930s: evidence accumulates for the widespread occurrence of quantitative (vs. either/or) traits and continuous variation (abundant hereditary variation governed by polygenic inheritance); i.e., can see a RANGE in phenotypes for POLYGENIC traits
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The Modern Synthesis (= NeoDarwinian Synthesis) *reconciles Darwin’s view of evolution by natural selection (ENS) with Mendelian genetics 1. Heredity is controlled by genes that obey Mendel’s rules of inheritance. 2. These genes are subject to random mutation which generates genetic variation (new alleles ) among individulas in a pop’n. 3. Natural selection “chooses” for alleles that confer reproductive success. This leads to small changes in the population from one generation to the next, and the accumulation of these ALLELES over time can lead to changes in the characteristics of populations (microevolution) or even the formation of new species (macroevolution). * This is a simplified view of the evolutionary process. Mutation is not the only source of genetic variation, and natural selection is not the only mechanism that leads to changes in gene frequencies.
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parents generation 1 offspring generation 1 parents generation 2 offspring generation 2 RECALL: Traits that enhance reproduction & survival become more common each generation * This population is evolving because we see allele frequency change from 1 generation to the next.
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The study of evolution, in its most simple form, is the study of changes in the frequencies of genes and gene combinations in a population .
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