How Populations Evolve Chapter 13 PDF

How Populations Evolve Chapter 13 Introduction more than 1.8 million species have been identified idea that species are descendants of ancestral species that were different from present-day ones environment plays a powerful role in evolution Darwin’s Theory of Evolution Voyage of the Beag...

How Populations Evolve Chapter 13 Introduction more than 1.8 million species have been identified idea that species are descendants of ancestral species that were different from present-day ones environment plays a powerful role in evolution Darwin’s Theory of Evolution Voyage of the Beagle collected specimens of South American plants and animals fossils resembled living species from the area in which they were found, and living species resembled other species from areas nearby Voyage of the Beagle Voyage of the Beagle Descent with Modification - all of life is connected by common ancestry - descendants have accumulated adaptations to changing environments Voyage of the Beagle Voyage of the Beagle evolution by means of natural selection as a theory, a widely accepted explanatory idea that - broader than a hypothesis - generates new hypotheses - supported by a large body of evidence Natural Selection, in a nutshell process through which populations of living organisms adapt and change over time - most fit genes will be passed on to the next generation - only the fittest genes will remain in the population Fossils = Evidence for Evolution fossils - imprints or remains of organisms that lived in the past - document differences - extinct species fossil record reveals the historical sequence in which organisms have evolved Fossils = Evidence for Evolution Transitional forms support Darwin’s theory many fossils link early extinct species with species living today Homologies = Evidence for Evolution descent with modification - remodeling process - related species can have characteristics that have an underlying similarity yet function differently - similarity resulting from common ancestry is known as homology Homologies = Evidence for Evolution Homologies = Evidence for Evolution homology helps explain why early stages of development vestigial structures, remnants of features that served important functions in the organism’s ancestors Homologies = Evidence for Evolution Homologies = Evidence for Evolution analogous structures: having same function but have different ancestry Homologies indicate patterns of descent Darwin proposed Natural Selection reasoned that if artificial selection can bring about so much change in a relatively short period of time, then natural selection could modify species considerably over hundreds or thousands of generations Darwin proposed Natural Selection Darwin proposed Natural Selection Darwin proposed Natural Selection three key points about evolution by means of natural selection: 1. natural selection occurs through interactions between individual organisms and the environment, individuals do not evolve 2. natural selection can amplify or diminish only heritable traits 3. evolution is not goal directed Natural Selection in action Natural Selection in action evolutionary adaptation reveal two important points about natural selection: - more of an editing process than a creative mechanism - contingent on time and place, favoring those heritable traits in a varying population that fit the current, local environment Evolution of Populations Mutation and Sexual Reproduction = genetic variation mutations are the ultimate source of the genetic variation that serves as raw material for evolution most of the genetic variation in a population results from the unique combination of alleles that each individual inherits Mutation and Sexual Reproduction = genetic variation crossing over independent orientation of homologous chromosomes random fertilization Evolution occurs in populations a population is a group of individuals of the same species that live in the same area and interbreed Evolution occurs in populations a population is a group of individuals of the same species that live in the same area and interbreed a gene pool consists of all copies of every type of allele, at every locus, in all members of the population Evolution occurs in populations Evolution occurs in populations a population is a group of individuals of the same species that live in the same area and interbreed a gene pool consists of all copies of every type of allele, at every locus, in all members of the population microevolution is a change in the frequencies of alleles in a population’s gene pool and evolution occurring on its smallest scale Evolution occurs in populations Hardy-Weinberg Equilibrium can test whether a population is evolving Hardy-Weinberg equilibrium states that allele (A and a) and genotype (AA, Aa, aa) frequencies will remain constant if: - NO selection Hardy-Weinberg Equilibrium can test whether a population is evolving Hardy-Weinberg equilibrium states that allele (A and a) and genotype (AA, Aa, aa) frequencies will remain constant if: - NO selection - NO mutation Hardy-Weinberg Equilibrium can test whether a population is evolving Hardy-Weinberg equilibrium states that allele (A and a) and genotype (AA, Aa, aa) frequencies will remain constant if: - NO selection - NO mutation - NO gene flow Hardy-Weinberg Equilibrium can test whether a population is evolving Hardy-Weinberg equilibrium states that allele (A and a) and genotype (AA, Aa, aa) frequencies will remain constant if: - NO selection - NO mutation - NO gene flow - NO non-random mating Hardy-Weinberg Equilibrium can test whether a population is evolving Hardy-Weinberg equilibrium states that allele (A and a) and genotype (AA, Aa, aa) frequencies will remain constant if: - NO selection - NO mutation - NO gene flow - NO non-random mating - large population Hardy-Weinberg Equilibrium Hardy-Weinberg Equilibrium genotype frequencies p2 + 2pq +q = 2 1 allele frequencies p+q=1 Hardy-Weinberg Equilibrium Aa Aa AA aa AA Aa aa Every individual must have one of three genotypes: AA Genotypes Genotype frequencies Sum of Genotype Frequencies Genotype frequency = number of individual with each genotype divided by the total possible genotypes. Every individual must have one of two alleles: Allele types Allele frequencies Sum of Allele Frequencies In the simplest case, allele frequency = frequencies of each allele in the population divided by the total possible alleles.  500 total frogs - 375 dark green SOLVE: § find genotype frequencies § find allele frequencies  500 total iguanas - 480 webbing SOLVE: § find genotype frequencies § find allele frequencies Hardy-Weinberg Equilibrium genotype frequencies are the same as in the parent population, the allele frequencies p and q are also the same the gene pool of this population is in a state of equilibrium Hardy-Weinberg Equilibrium is useful in public health science - estimate how many people carry alleles for certain inherited diseases Hardy-Weinberg Practice Problems You have sampled a population in which you know that the percentage of the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate the following: a. the frequency of the “aa” genotype b. the frequency of the “a” allele c. the frequency of the “A” allele d. the frequencies of the genotypes “AA” and “Aa” e. the frequencies of the two possible phenotypes if “A” is completely dominant over “a” You have sampled a population in which you know that the percentage of the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate the following: a. the frequency of the “aa” genotype You have sampled a population in which you know that the percentage of the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate the following: b. the frequency of the “a” allele You have sampled a population in which you know that the percentage of the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate the following: c. the frequency of the “A” allele You have sampled a population in which you know that the percentage of the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate the following: d. the frequencies of the genotypes “AA” and “Aa” You have sampled a population in which you know that the percentage of the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate the following: e. the frequencies of the two possible phenotypes if “A” is completely dominant over “a” Within a population of butterflies, the color brown (B) is dominant over the color white (b). And, 40% of all butterflies are white. Given this simple information, which is something that is very likely to be on the exam, calculate the following: a. the frequency of the recessive allele b. the frequency of the dominant allele c. the frequency of the heterozygous individuals Within a population of butterflies, the color brown (B) is dominant over the color white (b). And, 40% of all butterflies are white. Given this simple information, which is something that is very likely to be on the exam, calculate the following: a. the frequency of the recessive allele Within a population of butterflies, the color brown (B) is dominant over the color white (b). And, 40% of all butterflies are white. Given this simple information, which is something that is very likely to be on the exam, calculate the following: b. the frequency of the dominant allele Within a population of butterflies, the color brown (B) is dominant over the color white (b). And, 40% of all butterflies are white. Given this simple information, which is something that is very likely to be on the exam, calculate the following: c. the frequency of the heterozygous individuals Mechanisms of Microevolution Causes of evolutionary change 1. natural selection 2. genetic drift 3. gene flow Genetic Drift the drifting of frequency of an allele relative to that of the other alleles in the population two types of genetic drift: - bottleneck effect leads to a loss of genetic diversity when a population is greatly reduced Genetic Drift the drifting of frequency of an allele relative to that of the other alleles in the population two types of genetic drift: - bottleneck effect leads to a loss of genetic diversity when a population is greatly reduced - when a few individuals colonize an island or other new habitat, producing what is called the founder effect Natural Selection only mechanism that consistently leads to adaptive evolution relative fitness is the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals Explain how the phrase “survival of the fittest” differs from the biological definition of relative fitness. Natural Selection can alter variation in populations natural selection can affect the distribution of phenotypes in a population Natural Selection can alter variation in populations Sexual selection may lead to phenotypic differences sexual selection is a form of natural selection in which individuals with certain characteristics are more likely than other individuals to obtain mates secondary sex characteristics can give individuals an advantage in mating Types of sexual selection intrasexual selection in which individuals compete directly with members of the same sex for mates Types of sexual selection intrasexual selection in which individuals compete directly with members of the same sex for mates intersexual selection (between sexes) or mate choice, individuals of one sex (usually females) are choosy in selecting their mates Balancing selection preserves genetic variation balancing selection occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a population heterozygote advantage in which heterozygous individuals have greater reproductive success than either type of homozygote Balancing selection preserves genetic variation Natural Selection cannot fashion perfect organisms the evolution of organisms is constrained - selection can act only on existing variations - evolution is limited by historical constraints - adaptations are often compromises - chance, natural selection, and the environment interact You Should Now Be Able To: 1. Explain how Darwin’s voyage on the Beagle influenced his thinking. 2. Explain why the concept of evolution is regarded as a theory with great significance. 3. Explain how fossils form and why the fossil record is incomplete. 4. Explain how homologies, the fossil record, and molecular biology support evolution. 5. Explain how evolutionary trees are constructed and used to represent ancestral relationships. 6. Describe Darwin’s observations and inferences in developing the concept of natural selection. 6. Explain how the process of artificial selection influenced Darwin’s development of the idea of natural selection. 7. Explain why individuals cannot evolve and why evolution does not lead to perfectly adapted organisms. You Should Now Be Able To: 8. Describe two examples of natural selection known to occur in nature. 9. Explain how mutation and sexual reproduction produce genetic variation. 10. Explain why prokaryotes can evolve more quickly than eukaryotes. 11. Describe the five conditions required for the Hardy- Weinberg equilibrium. 12. Explain why the Hardy-Weinberg equilibrium is significant to understanding the evolution of natural populations and to public health science. 13. Define genetic drift and gene flow. Explain how the bottleneck effect and the founder effect influence microevolution. You Should Now Be Able To: 14. Distinguish between stabilizing selection, directional selection, and disruptive selection. Describe an example of each. 15. Define and compare intrasexual selection and intersexual selection. 16.Explain how antibiotic resistance evolves. 17.Explain how genetic variation is maintained in populations. 18.Explain why natural selection cannot produce perfection.