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Population GeneticsI. Population Genetics – the study of proportions of genes in a populationA. Macroevolution 1. Over a long period of time 2. Newer species replace old B. Microevolution 1. Change in population 2. Change in gene frequencies C. Darwin proposed “Natural Selection” 1. Individuals in a population which produce more surviving offspring than others D. Adaption – change in allelic frequency which favors survival E. Darwin 1. Adaption by natural selection is responsible for evolutionary change within a species. 2. Accumulation of these changes leads to new species (also results in change in allelic frequency) F. Blood Groups – 75 variables gene that account for blood groups G. Enzymes – limitless # of allelic combos 1. Polymorphism – locus w/ more variation than can be explained by mutation 2. Provide us with the ample raw materials for evolution H. Studied by the Hardy-Weinberg Equilibrium 1. Original proportions of genotypes in a population will remain constant from generation to generation 2. This based upon 5 basic conditions a) Large population b) No migration c) Random Mating d) No mutation e) No selection I. Agents that change the HW Equilibrium 1. Mutation 2. Migration 3. Genetic Drift 4. Non-random mating 5. Selection (only true agent of evolutionary change due to reliance on environment) J. Mutations 1. Ultimate source of variation 2. Makes evolution possible 3. Too slow to produce a major effect on HW equilibrium K. Migration 1. Effects are very diverse due to variety of movement, even as much as gamete movement 2. Gene pool – all alleles in a given population 3. Gene flow – genes moving from population to population L. Genetic Drift 1. Random change in allelic frequency of small populations 2. Small populations effect most 3. Loss of alleles due to lack of reproduction 4. Important in human evolution (we live in small groups) 5. Rare alleles & combinations can become greatly enhanced in new populations (Founder Principle) 6. Bottleneck Effect a) Serve reduction in size due to natural forces and changes in environment b) Survivors are a random sampling of original population c) Cheetahs – all cheetahs today descend from a small group of ancestors, so that they are all nearly genetically identical (susceptible to disease) M. Non-random Mating 1. Inbreeding 2. Increase homozygous traits 3. No change in allelic frequencies 4. Upsets HW N. Selection 1. More offspring w/ survivable traits are produced 2. Natural – environment determines offspring & \ # of genes in an individual population 3. Artificial – breeder selects traits 4. Key to Darwin’s Theory 5. Evolution occurs because of Natural Selection 6. Environment makes conditions for selection and thus drives the direction of evolution 7. Change HW by directly altering allelic frequency 8. Selection in Action a) Changes population depending on which genotypes are favored b) Directional selection – eliminating one extreme in favor of another c) Stabilizing selection – eliminating both extremes d) Disruptive selection – eliminating hybrids in favor of extremes Layout by J.T. Poirier © 2001 |