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CHAPTER 2 3
THE EVOLUTION OF POPULATIONS

OUTLINE

I. Population Genetics
A. The modern evolutionary synthesis integrated Darwinian selection and Mendelian inheritance
B. The genetic structure of a population is defined by its allele and genotype frequencies
C. The Hardy-Weinberg theorem describes a nonevolving population

II. Causes of Microevolution
A. Microevolution is a generation–to–generation change in a population’s allele or genotype frequencies
B. The five causes of microevolution are genetic drift, gene flow, mutation, nonrandom mating, and natural selection

III. Genetic Variation, the Substrate for Natural Selection
A. Genetic variation occurs within and between populations
B. Mutation and sexual recombination generate genetic variation
C. Diploidy and balanced polymorphism preserve variation

IV. Natural Selection as the Mechanisms of Adaptive Evolution
A. Evolutionary fitness is the relative contribution an individual makes to the gene pool of the next generation
B. The effect of selection on a varying characteristic can be stabilizing, directional, or diversifying
C. Sexual selection may lead to pronounced secondary differences between the sexes
D. Natural selection cannot fashion perfect organisms

OBJECTIVES

After reading this chapter and attending lecture, the student should be able to:
1. Explain how microevolutionary change can affect a gene pool.
2. In their own words, state the Hardy-Weinberg theorem.
3. Write the general Hardy-Weinberg equation and use it to calculate allele and genotype frequencies.
4. Explain the consequences of Hardy-Weinberg equilibrium.
5. Describe the usefulness of the Hardy-Weinberg model to population geneticists.
6. List the conditions a population must meet in order to maintain Hardy-Weinberg equilibrium.
7. Explain how genetic drift, gene flow, mutation, nonrandom mating and natural selection can cause microevolution.
8. Explain the role of population size in genetic drift.
9. Distinguish between the bottleneck effect and the founder effect.
10. Explain why mutation has little quantitative effect on a large population.
11. Describe how inbreeding and assortative mating affect a population's allele frequencies and genotype frequencies.
12. Explain, in their own words, what is meant by the statement that natural selection is the only agent of microevolution which is adaptive.
13. Describe the technique of electrophoresis and explain how it has been used to measure genetic variation within and between populations.
14. List some factors that can produce geographical variation among closely related populations.
15. Explain why even though mutation can be a source of genetic variability, it contributes a negligible amount to genetic variation in a population.
16. Give the cause of nearly all genetic variation in a population.
17. Explain how genetic variation may be preserved in a natural population.
18. In their own words, briefly describe the neutral theory of molecular evolution and explain how changes in gene frequency may be nonadaptive.
19. Explain the concept of relative fitness and its role in adaptive evolution.
20. Explain why the rate of decline for a deleterious allele depends upon whether the allele is dominant or recessive to the more successful allele.
21. Describe what selection acts on and what factors contribute to the overall fitness of a genotype.
22. Give examples of how an organism's phenotype may be influenced by the environment.
23. Distinguish among stabilizing selection, directional selection and diversifying selection.
24. Give at least four reasons why natural selection cannot breed perfect organisms.

KEY TERMS

population genetics microevolution geographical variation relative fitness
bottleneck effect cline stabilizing selection gene pool
population founder effect directional selection diversifying selection
species gene flow heterozygote advantage genetic structure
mutation hybrid vigor inbreeding frequency-dependent
sexual selection Hardy-Weinberg selection genetic equilibrium
natural selection neutral variation Darwinian fitness Industrial melanism
gene drift Eldridge-Gould transitional form punctuated equilibrium