Ch 13.10-13.15 Lecture Notes - Evolution

13.10 The Hardy-Weinberg Equation Can Test Whether a Population Is Evolving (1 of 3) The Hardy-Weinberg equilibrium states that allele and genotype frequencies will remain constant if: – a population is large – mating is random – there is no mutation, gene flow, or natural selection T...

13.10 The Hardy-Weinberg Equation Can Test Whether a Population Is Evolving (1 of 3) The Hardy-Weinberg equilibrium states that allele and genotype frequencies will remain constant if: – a population is large – mating is random – there is no mutation, gene flow, or natural selection The Hardy-Weinberg equation can be used to test whether evolution is occurring in a population. Copyright © 2020 Pearson Education, Inc. All Rights Reserved. 13.10 The Hardy-Weinberg Equation Can Test Whether a Population Is Evolving (2 of 3) To test the Hardy-Weinberg principle, let’s look at two generations of our imaginary iguana population. – Figure 13.10B shows the frequencies of alleles in the gene pool of the original population. – From these genotype frequencies, we can calculate the frequency of each allele in the population. Copyright © 2020 Pearson Education, Inc. All Rights Reserved. Figure 13.10a Copyright © 2020 Pearson Education, Inc. All Rights Reserved. Figure 13.10b Copyright © 2020 Pearson Education, Inc. All Rights Reserved. 13.10 The Hardy-Weinberg Equation Can Test Whether a Population Is Evolving (3 of 3) Fig 13.10C shows a Punnett square that uses these gamete allele frequencies and the rule of multiplication to calculate the frequencies of the three genotypes in the next generation. – Because the genotype frequencies are the same as in the parent population, the allele frequencies p and q are also the same. – Thus, the gene pool of this population is in a state of equilibrium—Hardy-Weinberg equilibrium. Copyright © 2020 Pearson Education, Inc. All Rights Reserved. Figure 13.10c Copyright © 2020 Pearson Education, Inc. All Rights Reserved. Mechanisms of Microevolution Copyright © 2020 Pearson Education, Inc. All Rights Reserved. 13.12 Natural Selection, Genetic Drift, and Gene Flow Can Cause Microevolution (1 of 2) The three main causes of evolutionary change are: 1. natural selection 2. ​genetic drift 3. ​gene flow Copyright © 2020 Pearson Education, Inc. All Rights Reserved. 13.12 Natural Selection, Genetic Drift, and Gene Flow Can Cause Microevolution (2 of 2) The bottleneck effect and founder effect lead to genetic drift: – The bottleneck effect leads to a loss of genetic diversity when a population is greatly reduced. – Genetic drift is also likely when a few individuals colonize an island or other new habitat, producing what is called the founder effect. Checkpoint question How might gene flow between populations living in different habitats actually interfere with each population’s adaptation to its local environment? Copyright © 2020 Pearson Education, Inc. All Rights Reserved. Figure 13.12a Copyright © 2020 Pearson Education, Inc. All Rights Reserved. 13.13 Natural Selection Only natural selection consistently leads to adaptive evolution—evolution that results in a better fit between organisms and their environment. Relative fitness is the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals. As a result of natural selection, favorable traits increase in a population. Copyright © 2020 Pearson Education, Inc. All Rights Reserved. 13.14 Visualizing the Concept: Natural Selection Can Alter Variation in a Population Natural selection can affect the distribution of phenotypes in a population in three ways: – Stabilizing selection favors intermediate phenotypes. – Directional selection shifts the overall makeup of the population by acting against individuals at one of the phenotypic extremes. – Disruptive selection typically occurs when environmental conditions vary in a way that favors individuals at both ends of a phenotypic range over individuals with intermediate phenotypes. Copyright © 2020 Pearson Education, Inc. All Rights Reserved. Figure 13.14 Copyright © 2020 Pearson Education, Inc. All Rights Reserved. Figure 13.14_1 Copyright © 2020 Pearson Education, Inc. All Rights Reserved. Figure 13.14_2 Copyright © 2020 Pearson Education, Inc. All Rights Reserved. Figure 13.14_3 Copyright © 2020 Pearson Education, Inc. All Rights Reserved. 13.14 Visualizing The Concept: Natural Selection Can Alter Variation in a Population in Three Ways (2 of 2) Checkpoint question What type of selection probably resulted in the color variations evident in the garter snakes seen above? Copyright © 2020 Pearson Education, Inc. All Rights Reserved. 13.15 Sexual Selection May Lead to Phenotypic Differences Between Males and Females (1 of 3) 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. Copyright © 2020 Pearson Education, Inc. All Rights Reserved. Figure 13.15a Copyright © 2020 Pearson Education, Inc. All Rights Reserved. 13.15 Sexual Selection May Lead to Phenotypic Differences Between Males and Females (2 of 3) In some species, intrasexual selection occurs, in which individuals compete directly with members of the same sex for mates. In a more common type of sexual selection, called intersexual selection (between sexes) or mate choice, individuals of one sex (usually females) are choosy in selecting their mates. Copyright © 2020 Pearson Education, Inc. All Rights Reserved. 13.15 Sexual Selection May Lead to Phenotypic Differences Between Males and Females (3 of 3) Checkpoint question Males with the most elaborate ornamentation may garner the most mates. How might choosing such a mate be advantageous to a female? Copyright © 2020 Pearson Education, Inc. All Rights Reserved. Figure 13.15b Copyright © 2020 Pearson Education, Inc. All Rights Reserved. Figure 13.15c Copyright © 2020 Pearson Education, Inc. All Rights Reserved. Natural Selection Cannot Fashion Perfect Organisms (1 of 2) The evolution of organisms is constrained: 1. Selection can act only on existing variations. ​New, advantageous alleles do not arise on demand. 2. ​Evolution is limited by historical constraints. Evolution co-opts existing structures and adapts them to new situations. 3. ​Adaptations are often compromises. The same structure often performs many functions. 4. ​Chance, natural selection, and the environment interact. Environments often change unpredictably. Copyright © 2020 Pearson Education, Inc. All Rights Reserved. You Should Now Be Able to (1 of 4) 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. Copyright © 2020 Pearson Education, Inc. All Rights Reserved. You Should Now Be Able to (2 of 4) 6. Describe Darwin’s observations and inferences in developing the concept of natural selection. 7. Explain how the work of Thomas Malthus and the process of artificial selection influenced Darwin’s development of the idea of natural selection. 8. Explain why individuals cannot evolve and why evolution does not lead to perfectly adapted organisms. 9. Describe two examples of natural selection known to occur in nature. Copyright © 2020 Pearson Education, Inc. All Rights Reserved. You Should Now Be Able to (3 of 4) 10.Explain how mutation and sexual reproduction produce genetic variation. 11.Explain why prokaryotes can evolve more quickly than eukaryotes. 12.Describe the five conditions required for the Hardy- Weinberg equilibrium. 13.Explain why the Hardy-Weinberg equilibrium is significant to understanding the evolution of natural populations and to public health science. 14.Define genetic drift and gene flow. Explain how the bottleneck effect and the founder effect influence microevolution. Copyright © 2020 Pearson Education, Inc. All Rights Reserved. You Should Now Be Able to (4 of 4) 15.Distinguish between stabilizing selection, directional selection, and disruptive selection. Describe an example of each. 16.Define and compare intrasexual selection and intersexual selection. 17.Explain how antibiotic resistance evolves. 18.Explain how genetic variation is maintained in populations. 19.Explain why natural selection cannot produce perfection. Copyright © 2020 Pearson Education, Inc. All Rights Reserved.