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BIOLOGY CONCEPTS & CONNECTIONS Fourth Edition Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor CHAPTER 13 How Populations Evolve Modules 13.4 – 13.12 From PowerPoint® Lectures for Biology: Concepts & Connections Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • 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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • 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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings – Example of artificial selection in animals: dog breeding German shepherd Yorkshire terrier English springer spaniel Mini-dachshund Golden retriever Hundreds to thousands of years of breeding (artificial selection) Ancestral dog Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 13.4B • These five canine species evolved from a common ancestor through natural selection African wild dog Coyote Fox Wolf Jackal Thousands to millions of years of natural selection Ancestral canine Figure 13.4C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • The evolution of insecticide resistance is an example of natural selection in action Insecticide application Chromosome with gene conferring resistance to insecticide Additional applications of the same insecticide will be less effective, and the frequency of resistant insects in the population will grow Survivor Figure 13.5B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 13.6 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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • We can follow alleles in a population to observe if Hardy-Weinberg equilibrium exists Phenotypes Genotypes WW Ww ww Number of animals (total = 500) 320 160 20 Genotype frequencies 320/ 500 = 0.64 Number of alleles in gene pool (total = 1,000) 640 W Allele frequencies 800/ 1,000 160/ 500 20/ = 0.32 160 W + 160 w = 0.8 W 200/ 1,000 500 = 0.04 40 w = 0.2 w Figure 13.8B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Recombination of alleles from parent generation SPERM EGGS WW p2 = 0.64 WW qp = 0.16 Ww pq = 0.16 ww q2 = 0.04 Next generation: Genotype frequencies 0.64 WW Allele frequencies 0.32 Ww 0.8 W 0.04 ww 0.2 w Figure 13.8C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 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 diseasecausing alleles in the human population – Example: phenylketonuria (PKU) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 13.10 Five conditions are required for HardyWeinberg 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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 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 Original population Bottlenecking event Surviving population Figure 13.11A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings – or the founder effect Figure 13.11B, C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Gene flow can change a gene pool due to the movement of genes into or out of a population • Mutation changes alleles • Natural selection leads to differential reproductive success Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 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 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings