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Population Genetics & Evolution Warm-up What are the 3 ways that sexual reproduction produces genetic diversity? Why is this important for evolution? Warm-up At which level does natural selection at— individuals or populations? At which level does evolution act—individuals or populations? Vocab • Gene pool: all of the alleles for all genes in all the members of the population – What’s in the gene pool for the beetles? – Can calculate allele and frequencies • Fixed allele: all members of a population only have 1 allele for a particular trait – The more fixed alleles a population has, the LOWER the species’ diversity – Example of a fixed allele in the beetle population… Hardy-Weinberg Theorem Hardy-Weinberg Theorem: The allele and genotype frequencies of a population will remain constant from generation to generation …UNLESS they are acted upon by certain forces Equilibrium = allele and genotype frequencies remain constant Conditions for Hardy-Weinberg equilibrium 1. 2. 3. 4. 5. No mutations. Random mating. No natural selection. Extremely large population size. No gene flow. If at least one of these conditions is NOT met, then the population is EVOLVING! Microevolution vs Macroevolution: • Microevolution: A change in allele frequencies in a population over generations. Creates changes (adaptations) that are confined to a particular gene pool or population. • Macroevolution: Occurs over geologic time above the level of the species. The fossil record reflects macroevolution. It results from microevolution taking place over many generations and helps define taxa. Minor Causes of Evolution: #1 - Mutations – Rare, very small changes in allele frequencies #2 - Nonrandom mating – The idea that mating is NOT random! (females are “choosy”) • • https://www.youtube.com/watch?v=KW8GX2n4qbY https://www.youtube.com/watch?v=L54bxmZy_NE Minor Causes of Evolution: #1 - Mutations – Rare, very small changes in allele frequencies #2 - Nonrandom mating – Affect genotypes, but not allele frequencies Major Causes of Evolution: • Natural selection, genetic drift, gene flow (#3-5) Major Causes of Evolution #3 – Natural Selection – Individuals with variations better suited to environment pass more alleles to next generation 4- Genetic drift – a change in allele frequencies due to chance, not natural selection. • Usually occurs in smaller populations cut off from main population. (No gene flow) • Reduces genetic variation. Genetic Drift: allele frequencies “drift” away from original population’s. The smaller a population, the more vulnerable it is to genetic drift. • How might this affect endangered species? The Bottleneck Effect – when a population has been dramatically reduced, and the gene pool is no longer reflective of the gene pool of the original population. Founder effect – when a small number of individuals colonize a new area; new gene pool not reflective of original population The Fugate family Kentucky's Troublesome CreekExtra credit Reduction of genetic variation within a given population can increase the differences between populations of the same species. The Serval from Africa, the Canada Lynx from N. America and Margay from S. America Michael Major Causes of Evolution #5 – Gene Flow (migration) – Movement of fertile individuals between populations – Gain/lose alleles – Reduces genetic differences between populations (slows down speciation) Gene flow Conditions for Hardy-Weinberg equilibrium 1. 2. 3. 4. 5. No mutations. Random mating. No natural selection. Extremely large population size. No gene flow. If at least one of these conditions is NOT met, then the population is EVOLVING! Crash Course Review • https://www.youtube.com/watch?v=WhFKPa RnTdQ • (1:04 – 4:45) Model 1 Model 2