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CHAPTER 13 How Populations Evolve

CHAPTER 13 How Populations Evolve. Modules 13.4 – 13.12. DARWIN’S THEORY AND THE MODERN SYNTHESIS. 13.4 Darwin proposed natural selection as the mechanism of evolution. Darwin observed that organisms produce more offspring than the environment can support

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CHAPTER 13 How Populations Evolve

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  1. CHAPTER 13How Populations Evolve Modules 13.4 – 13.12

  2. DARWIN’S THEORY AND THE MODERN SYNTHESIS 13.4 Darwin proposed natural selection as the mechanism of evolution • Darwin observed that • organisms produce more offspring than the environment can support • organisms vary in many characteristics • these variations can be inherited

  3. Darwin concluded that individuals best suited for a particular environment are more likely to survive and reproduce than those less well adapted • Darwin saw natural selection as the basic mechanism of evolution • As a result, the proportion of individuals with favorable characteristics increases • Populations gradually change in response to the environment

  4. Darwin also saw that when humans choose organisms with specific characteristics as breeding stock, they are performing the role of the environment • This is called artificial selection • Example of artificial selection in plants: five vegetables derived from wild mustard Figure 13.4A

  5. Example of artificial selection in animals: dog breeding English springerspaniel German shepherd Yorkshire terrier Mini-dachshund Golden retriever Hundreds tothousands of yearsof breeding(artificial selection) Ancestral dog Figure 13.4B

  6. These five canine species evolved from a common ancestor through natural selection African wilddog Coyote Fox Wolf Jackal Thousands tomillions of yearsof natural selection Ancestral canine Figure 13.4C

  7. 13.5 Connection: Scientists can observe natural selection in action • Evolutionary adaptations have been observed in populations of birds, insects, and many other organisms • Example: camouflage adaptations of mantids that live in different environments Figure 13.5A

  8. The evolution of insecticide resistance is an example of natural selection in action Insecticideapplication Chromosome with geneconferring resistanceto insecticide Additionalapplications of thesame insecticide willbe less effective, andthe frequency ofresistant insects inthe populationwill grow Survivor Figure 13.5B

  9. 13.6 Populations are the units of evolution • A species is a group of populations whose individuals can interbreed and produce fertile offspring • Human populations tend to concentrate locally, as this satellite photograph of North America shows • The modern synthesis connects Darwin’s theory of natural selection with population genetics Figure 13.6

  10. 13.7 Microevolution is change in a population’s gene pool over time • A gene pool is the total collection of genes in a population at any one time • Microevolution is a change in the relative frequencies of alleles in a gene pool

  11. 13.8 The gene pool of a nonevolving population remains constant over the generations • Hardy-Weinberg equilibrium states that the shuffling of genes during sexual reproduction does not alter the proportions of different alleles in a gene pool • To test this, let’s look at an imaginary, nonevolving population of blue-footed boobies Webbing No webbing Figure 13.8A

  12. Phenotypes • We can follow alleles in a population to observe if Hardy-Weinberg equilibrium exists Genotypes WW Ww ww Number of animals(total = 500) 320 160 20 Genotype frequencies 320/500 = 0.64 160/500 = 0.32 20/500 = 0.04 Number of allelesin gene pool(total = 1,000) 640 W 160 W + 160 w 40 w Allele frequencies 800/1,000 = 0.8 W 200/1,000 = 0.2 w Figure 13.8B

  13. Recombinationof alleles fromparent generation W sperm p = 0.8 W egg p = 0.8 SPERM EGGS WW p2 = 0.64 w sperm q = 0.2 w egg q = 0.2 WW qp = 0.16 Ww pq = 0.16 ww q2 = 0.04 Next generation: Genotype frequencies 0.64 WW 0.32 Ww 0.04 ww Allele frequencies 0.8 W 0.2 w Figure 13.8C

  14. 13.9 Connection: The Hardy-Weinberg equation is useful in public health science • Public health scientists use the Hardy-Weinberg equation to estimate frequencies of disease-causing alleles in the human population • Example: phenylketonuria (PKU)

  15. 13.10 Five conditions are required for Hardy-Weinberg equilibrium • The population is very large • The population is isolated • Mutations do not alter the gene pool • Mating is random • All individuals are equal in reproductive success

  16. 13.11 There are several potential causes of microevolution • Genetic drift is a change in a gene pool due to chance • Genetic drift can cause the bottleneck effect Originalpopulation Bottleneckingevent Survivingpopulation Figure 13.11A

  17. or the founder effect Figure 13.11B, C

  18. Mutation changes alleles • Natural selection leads to differential reproductive success • Gene flow can change a gene pool due to the movement of genes into or out of a population

  19. 13.12 Adaptive change results when natural selection upsets genetic equilibrium • Natural selection results in the accumulation of traits that adapt a population to its environment • If the environment should change, natural selection would favor traits adapted to the new conditions

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