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Chapter 16 Population Genetics and Speciation Table of Contents Section 1 Genetic Equilibrium Section 2 Disruption of Genetic Equilibrium Section 3 Formation of Species Chapter 16 Section 1 Genetic Equilibrium Standards SPI 3210.5.1 Compare and contrast the structural, functional, and behavioral adaptations of animals or plants found in different environments. SPI 3210.5.2 Recognize the relationship between form and function in living things. SPI 3210.5.3 Recognize the relationships among environmental change, genetic variation, natural selection, and the emergence of a new species. SPI 3210.5.4 Describe the relationship between the amount of biodiversity and the ability of a population to adapt to a changing environment. SPI 3210.5.5 Apply evidence from the fossil record, comparative anatomy, amino acid sequences, and DNA structure that support modern classification systems. SPI 3210.5.6 Infer relatedness among different organisms using modern classification systems. Chapter 16 Section 1 Genetic Equilibrium Objectives • Identify traits that vary in populations and that may be studied. • Explain the importance of the bell curve to population genetics. • Compare three causes of genetic variation in a population. • Calculate allele frequency and phenotype frequency. • Explain Hardy-Weinberg genetic equilibrium. Chapter 16 Section 1 Genetic Equilibrium Variation of Traits Within a Population • Population biologists study many different traits in populations, such as size and color. Chapter 16 Section 1 Genetic Equilibrium 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. Chapter 16 Section 1 Genetic Equilibrium The Gene Pool • The total genetic information available in a population is called the gene pool. Chapter 16 Section 1 Genetic Equilibrium 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. Chapter 16 Section 1 Genetic Equilibrium 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. Chapter 16 Section 1 Genetic Equilibrium The Hardy-Weinberg Genetic Equilibrium • Allele frequencies in the gene pool do not change unless acted upon by certain forces. • Hardy-Weinberg genetic equilibrium is a theoretical model of a population in which no evolution occurs and the gene pool of the population is stable. Chapter 16 Section 1 Genetic Equilibrium Phenotype Frequency Chapter 16 Section 2 Disruption of Genetic Equilibrium Objectives • List five conditions under which evolution may take place. • Explain how migration can affect the genetics of populations. • Explain how genetic drift can affect populations of different sizes. • Contrast the effects of stabilizing selection, directional selection, and disruptive selection on populations over time. • Identify examples of nonrandom mating. Chapter 16 Section 1 Genetic Equilibrium Standards SPI 3210.5.1 Compare and contrast the structural, functional, and behavioral adaptations of animals or plants found in different environments. SPI 3210.5.2 Recognize the relationship between form and function in living things. SPI 3210.5.3 Recognize the relationships among environmental change, genetic variation, natural selection, and the emergence of a new species. SPI 3210.5.4 Describe the relationship between the amount of biodiversity and the ability of a population to adapt to a changing environment. SPI 3210.5.5 Apply evidence from the fossil record, comparative anatomy, amino acid sequences, and DNA structure that support modern classification systems. SPI 3210.5.6 Infer relatedness among different organisms using modern classification systems. Chapter 16 Section 2 Disruption of Genetic Equilibrium 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. Chapter 16 Section 2 Disruption of Genetic Equilibrium Gene Flow • Emigration and immigration cause gene flow between populations and can thus affect gene frequencies. Chapter 16 Section 2 Disruption of Genetic Equilibrium Genetic Drift • Genetic drift is a change in allele frequencies due to random events. • Genetic drift operates most strongly in small populations. Chapter 16 Section 2 Disruption of Genetic Equilibrium Nonrandom Mating • Mating is nonrandom whenever individuals may choose partners. Chapter 16 Section 2 Disruption of Genetic Equilibrium 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. Chapter 16 Section 2 Disruption of Genetic Equilibrium Natural Selection • Natural selection can influence evolution in one of three general patterns. Chapter 16 Section 2 Disruption of Genetic Equilibrium Natural Selection, continued • Stabilizing Selection – Stabilizing selection favors the formation of average traits. Chapter 16 Section 2 Disruption of Genetic Equilibrium Natural Selection, continued • Disruptive Selection – Disruptive selection favors extreme traits rather than average traits. Chapter 16 Section 2 Disruption of Genetic Equilibrium Natural Selection, continued • Directional Selection – Directional selection favors the formation of more-extreme traits. Chapter 16 Two Kinds of Selection Section 2 Disruption of Genetic Equilibrium Chapter 16 Section 3 Formation of Species Objectives • Relate the biological species concept to the modern definition of species. • Explain how the isolation of populations can lead to speciation. • Compare two kinds of isolation and the pattern of speciation associated with each. • Contrast the model of punctuated equilibrium with the model of gradual change. Chapter 16 Section 1 Genetic Equilibrium Standards SPI 3210.5.1 Compare and contrast the structural, functional, and behavioral adaptations of animals or plants found in different environments. SPI 3210.5.2 Recognize the relationship between form and function in living things. SPI 3210.5.3 Recognize the relationships among environmental change, genetic variation, natural selection, and the emergence of a new species. SPI 3210.5.4 Describe the relationship between the amount of biodiversity and the ability of a population to adapt to a changing environment. SPI 3210.5.5 Apply evidence from the fossil record, comparative anatomy, amino acid sequences, and DNA structure that support modern classification systems. SPI 3210.5.6 Infer relatedness among different organisms using modern classification systems. Chapter 16 Section 3 Formation of Species 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. Chapter 16 Section 3 Formation of Species Isolation and Speciation • Geographic Isolation – Geographic isolation results from the separation of population subgroups by geographic barriers. Chapter 16 Section 3 Formation of Species Geographic Isolation Click below to watch the Visual Concept. Chapter 16 Section 3 Formation of Species Isolation and Speciation, continued • Allopatric Speciation – Geographic isolation may lead to allopatric speciation. Chapter 16 Section 3 Formation of Species Isolation and Speciation, continued • Reproductive Isolation – Reproductive isolation results from the separation of population subgroups by barriers to successful breeding. Chapter 16 Section 3 Formation of Species Reproductive Isolation Click below to watch the Visual Concept. Chapter 16 Section 3 Formation of Species Isolation and Speciation, continued • Sympatric Speciation – Reproductive isolation within the same geographic area is known as sympatric speciation. Chapter 16 Section 3 Formation of Species 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. Chapter 16 Section 3 Formation of Species Comparing Punctuated Equilibrium and Gradualism