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AP Biology Mrs. Farish Name ______________________________ Chapter 23: The Evolution of Populations Study Questions 1. Predict how microevolutionary change can affect a gene pool. 2. Demonstrate that a population not at equilibrium requires only one generation of random mating to establish Hardy-Weinberg equilibrium. 3. Describe the conditions that a population must meet in order to maintain Hardy-Weinberg equilibrium. 4. Distinguish between the bottleneck effect and the founder effect. 5. Explain why even though mutation can be a source of genetic variability, it contributes a negligible amount to genetic variation in a population. 6. Explain the concept of relative fitness and its role in adaptive evolution. 7. Why does the rate of decline for a deleterious allele depend upon whether the allele is dominant or recessive to the more successive allele? 8. Distinguish among stabilizing selection, directional selection, and diversifying selection. 9. How can sexual dimorphism influence evolutionary change? 10. In your own words, explain why natural selection cannot breed perfect organisms. 1. Predict how microevolutionary change can affect a gene pool. Microevolution is evolutionary change below the species level; change in the genetic makeup of a population from generation to generation. Genetic Drift – unpredictable fluctuations in allele frequencies from one generation to the next because of a population’s finite size i. Bottle neck effect – gen. Drift resulting from the reduction of a population, typically by a natural disaster, such that the surviving population is not longer genetically representative of the original population ii. Founder effect – gen. Drift that occurs when a few individuals become isolated from a larger population, with the result that the new population’s gene pool is not reflective of the original population Gene flow- genetic additions to or subtractions from a population resulting from the movement of fertile individuals or gametes. Mutation- change in DNA of a gene creating genetic diversity Non-random mating: Inbreeding- mating of genetically similar individuals, which tends to increase the number of individuals that are homozygous for a trait and therefore increase the appearance of recessive traits. Assortive matingi. (+) mate with individuals that are genetically similar ii. (-) mate with individuals that are different Natural Selection- differential success in the reproduction of different phenotypes resulting from the interaction of organisms with their environment. Evolution occurs when natural selection causes changes in relative frequencies of alleles in the gene pool. 2. Demonstrate that a population not at equilibrium requires only one generation of random mating to establish Hardy-Weinberg equilibrium. 3. Describe the conditions that a population must meet in order to maintain HardyWeinberg equilibrium. Extremely large population size – The smaller the population, the greater the role played by chance fluctuations in allele frequencies from one generation to the next (genetic drift) No gene flow – Gene flow (transfer of alleles between populations) can alter allele frequencies No mutations – By introducing or removing genes from chromosomes or by changing one allele into another, mutations modify the gene pool Random mating – If individuals preferentially choose mates with certain genotypes, including close relatives (inbreeding), random mixing of gametes does not occur. No natural selection – Differential survival and reproductive success of individuals carrying different genotypes will alter allele frequencies. 4. Distinguish between the bottleneck effect and the founder effect. i. Bottle neck effect – gen. Drift resulting from the reduction of a population, typically by a natural disaster, such that the surviving population is not longer genetically representative of the original population ii. Founder effect – gen. Drift that occurs when a few individuals become isolated from a larger population, with the result that the new population’s gene pool is not reflective of the original population 5. Explain why even though mutation can be a source of genetic variability, it contributes a negligible amount to genetic variation in a population. Most mutations occur in somatic cells and are lost when the individual dies. Only mutations in cell lines that produce gametes can be passed to offspring, and only a small fraction of these spread through populations. Organisms reflect thousands of generations of past selection, and a single mutation is not very likely to improve the genome. 6. Explain the concept of relative fitness and its role in adaptive evolution. Relative fitness is the contribution of one genotype to the next generation compared to that of alternative genotypes for the same locus. Adaptive evolution involves adaptations (such as a higher reproductive rate in wildflowers due to brighter colors or fragrance to attract pollinators) that serve as genetic contributions to the gene pool of the next generation. 7. Why does the rate of decline for a deleterious allele depend upon whether the allele is dominant or recessive to the more successive allele? 8. Distinguish among stabilizing selection, directional selection, and diversifying selection. Stabilizing selection – natural selection that favors intermediate variants by acting against extreme phenotypes. Directional selection – natural selection that favors individuals at one end of the phenotypic range. Disruptive selection – natural selection that favors individuals on both extremes of a phenotypic range over intermediate phenotypes. 9. How can sexual dimorphism influence evolutionary change? Sexual dimorphism is a case of polymorphism based on the distinction between the secondary sex characteristics of males and females. For example, if females choose their mates (intersexual selection), she will choose based on a certain appearance or behavior. As a result, she perpetuates the alleles that influenced her to make that choice, allwing a male with an especially showy phenotype to pass on his alleles to offspring. 10. In your own words, explain why natural selection cannot breed perfect organisms. Evolution is limited by historical constraints. Adaptations are often compromises. Chance and natural selection interact. Selection can edit only existing variations.