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Agents of Evolutionary Change Or Disruption of Genetic Equilibrium Last Class Chapter 15 Review Fossils Evolutionary Theorists Evolutionary Evidence Processes of Evolution Build-A-Beast Workshop (Due Monday Oct 5, along with presentation) Test – Evolution- Wednesday Oct 7 Today We will discuss how Evolution occurs in populations Agents of Evolutionary change AKA Disruption of Genetic Equilibrium Genetic Drift Activity Computer Lab time But First… Evolution Quiz! Everything off your tables except for a writing utensil! 5 min (shouldn’t take too much longer…) Back to the Lesson… But First… Let’s do a Think- Pair- Share What traits would a NON-EVOLVING population have? What factors would keep this population from evolving? Hardy-Weinberg Genetic Equilibrium Of course we know by now, that populations do evolve… but typically not at any rate which we can really see. populations tend to remain the same from generation to generation, unless enacted on by an outside influence This is what is known as the Hardy-Weinberg Genetic Equilibrium (HWE) Hardy-Weinberg Genetic Equilibrium It is based on a set of assumptions about a hypothetical and ideal population that is not evolving; 1. No Net Mutations occur 2. Individuals do not enter or leave the population 3. The population is large (ideally, infinitely) 4. Individuals mate randomly 5. Selection does not occur HWE Continued Of course, there is no population like that… The HWE is used to measure the rate of evolutionary change in a population, by comparing it to an ideal, never evolving population Let’s Look Back at the “Ideal” NonEvolving Population… 1. No Net Mutations occur 2. Individuals do not enter or leave the population 3. The population is large (ideally, infinitely) 4. Individuals mate randomly 5. Selection does not occur An Evolutionary change in a population would therefore involve one of these changes to occur. Agents of Evolutionary change Mutation, Genetic Drift, Migration (Gene Flow), Non-Random Mating, Natural Selection Mutations We have learned how mutations are copying errors during DNA replication. Mutations can happen in different ways: Substitutions ACTGCGA ACTGCCT (sickle cell anemia) Insertion ACTGCGA ACTGACGA Deletions ACTGCGA ACTCGA G Insertions and Deletions lead to Frameshifts Mutations (cont’d) Types of mutations: Neutral Most common. Change in DNA sequence that has no affect on protein synthesis Harmful Second most common: change in DNA sequence leads to harmful trait Beneficial Least common, mutation leads to trait which serves beneficial to organism. Driving force of evolution Genetic Drift The Hardy-Weinberg equilibrium does not hold for small or medium populations Genetic drift is the phenomenon by which allele (genetic traits) frequencies in a population change as a result of RANDOM events or CHANCE In a small population the FAILURE or GREATER THAN NORMAL RATE of one organism to reproduce can significantly disrupt gene frequency Loss in genetic variation means there is nothing for natural selection to act upon - Positive or Negative traits can’t be selected if all genes across population are similar Genetic Drift- Bottleneck effect Genetic Drift- Founders Effect Now let’s see genetic drift in action… In groups of 3, grab one cup of candy, and one worksheet Follow directions, and complete questions When finished In your Notebook Explain in your own words the positives and negatives of mutations on an INDIVIDUAL. Why might mutations be more beneficial on a POPULATION? Why are species in danger of extinction if there is no variation in allele (gene) frequencies in the population? Next Class Look at the other 3 agents of Evolutionary change Migration (Gene Flow) Non-random mating Natural Selection