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Table of Contents

This chapter explores the concepts of genetic equilibrium and disruption in population genetics and speciation. It covers topics such as variation of traits within a population, the gene pool, Hardy-Weinberg genetic equilibrium, and the effects of migration, genetic drift, nonrandom mating, and natural selection on gene frequencies. Additionally, it delves into the formation of species through isolation and the patterns of speciation.

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Table of Contents

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  1. Population Genetics and Speciation Chapter 16 Table of Contents Section 1 Genetic Equilibrium Section 2 Disruption of Genetic Equilibrium Section 3 Formation of Species

  2. Section 1 Genetic Equilibrium Chapter 16 Objectives • Identifytraits that vary in populations and that may be studied. • Explainthe importance of the bell curve to population genetics. • Compare three causes of genetic variation in a population. • Calculate allele frequency and phenotype frequency. • ExplainHardy-Weinberg genetic equilibrium.

  3. Section 1 Genetic Equilibrium Chapter 16 Variation of Traits Within a Population • Population biologists study many different traits in populations, such as size and color.

  4. Section 1 Genetic Equilibrium Chapter 16 Variation of Traits Within a Population, continued • Causes of Variation • Traits vary and can be mapped along a bell curve, which shows that most individuals have average traits, whereas a few individuals have extreme traits. • Variations in genotype arise by mutation,recombination, and the random pairing of gametes.

  5. Section 1 Genetic Equilibrium Chapter 16 The Gene Pool • The total genetic information available in a population is called thegene pool.

  6. Section 1 Genetic Equilibrium Chapter 16 The Gene Pool, continued • Allele frequency is determined by dividing the total number of a certain allele by the total number of alleles of all types in the population.

  7. Section 1 Genetic Equilibrium Chapter 16 The Gene Pool, continued • Predicting Phenotype • Phenotype frequency is equal to the number of individuals with a particular phenotype divided by the total number of individuals in the population.

  8. Section 1 Genetic Equilibrium Chapter 16 The Hardy-Weinberg Genetic Equilibrium • Allele frequencies in the gene pool do not change unless acted upon by certain forces. • Hardy-Weinberg genetic equilibriumis a theoretical model of a population in which no evolution occurs and the gene pool of the population is stable.

  9. Section 1 Genetic Equilibrium Chapter 16 Phenotype Frequency

  10. Section 2 Disruption ofGenetic Equilibrium Chapter 16 Objectives • Listfive conditions under which evolution may take place. • Explain how migration can affect the genetics of populations. • Explainhow genetic drift can affect populations of different sizes. • Contrastthe effects of stabilizing selection, directional selection, and disruptive selection on populations over time. • Identify examples of nonrandom mating.

  11. Section 2 Disruption ofGenetic Equilibrium Chapter 16 Mutation • Evolution may take place when populations are subject to genetic mutations, gene flow, genetic drift, nonrandom mating, or natural selection. • Mutations are changes in the DNA.

  12. Section 2 Disruption ofGenetic Equilibrium Chapter 16 Gene Flow • Emigration and immigration cause gene flow between populations and can thus affect gene frequencies.

  13. Section 2 Disruption ofGenetic Equilibrium Chapter 16 Genetic Drift • Genetic driftis a change in allele frequencies due to random events. • Genetic drift operates most strongly in small populations.

  14. Section 2 Disruption ofGenetic Equilibrium Chapter 16 Nonrandom Mating • Mating is nonrandom whenever individuals may choose partners.

  15. Section 2 Disruption ofGenetic Equilibrium Chapter 16 Nonrandom Mating, continued • Sexual Selection • Sexual selection occurs when certain traits increase an individual’s success at mating. • Sexual selection explains the development of traits that improve reproductive success but that may harm the individual.

  16. Section 2 Disruption ofGenetic Equilibrium Chapter 16 Natural Selection • Natural selectioncan influence evolution in one of three general patterns.

  17. Section 2 Disruption ofGenetic Equilibrium Chapter 16 Natural Selection, continued • Stabilizing Selection • Stabilizing selectionfavors the formation of average traits.

  18. Section 2 Disruption ofGenetic Equilibrium Chapter 16 Natural Selection, continued • Disruptive Selection • Disruptive selectionfavors extreme traits rather than average traits.

  19. Section 2 Disruption ofGenetic Equilibrium Chapter 16 Natural Selection, continued • Directional Selection • Directional selectionfavors the formation of more-extreme traits.

  20. Section 2 Disruption ofGenetic Equilibrium Chapter 16 Two Kinds of Selection

  21. Section 3 Formation of Species Chapter 16 Objectives • Relatethe biological species concept to the modern definition of species. • Explain how the isolation of populations can lead to speciation. • Comparetwo kinds of isolation and the pattern of speciation associated with each. • Contrastthe model of punctuated equilibrium with the model of gradual change.

  22. Section 3 Formation of Species Chapter 16 The Concept of Species • According to the biological species concept, a species is a population of organisms that can successfully interbreed but cannot breed with other groups.

  23. Section 3 Formation of Species Chapter 16 Isolation and Speciation • Geographic Isolation • Geographic isolation results from the separation of population subgroups by geographic barriers.

  24. Section 3 Formation of Species Chapter 16 Geographic Isolation Click below to watch the Visual Concept. Visual Concept

  25. Section 3 Formation of Species Chapter 16 Isolation and Speciation, continued • Allopatric Speciation • Geographic isolation may lead to allopatric speciation.

  26. Section 3 Formation of Species Chapter 16 Isolation and Speciation, continued • Reproductive Isolation • Reproductive isolation results from the separation of population subgroups by barriers to successful breeding.

  27. Section 3 Formation of Species Chapter 16 Reproductive Isolation Click below to watch the Visual Concept. Visual Concept

  28. Section 3 Formation of Species Chapter 16 Isolation and Speciation, continued • Sympatric Speciation • Reproductive isolation within the same geographic area is known as sympatric speciation.

  29. Section 3 Formation of Species Chapter 16 Rates of Speciation • In the gradual model of speciation (gradualism), species undergo small changes at a constant rate. • Under punctuated equilibrium, new species arise abruptly, differ greatly from their ancestors, and then change little over long periods.

  30. Section 3 Formation of Species Chapter 16 Comparing Punctuated Equilibrium and Gradualism Click below to watch the Visual Concept. Visual Concept

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