Chapter 22: Descent with Modification: A Darwinian View of Lift Name Period Chapter 22: Descent wffh Modification: A Darwinian View of Life As you study this chaptel read several paragraphs at a time to catch the flow of ideas and understan(i the reasoning that is being described. In some places, the text describes a narrative or story regardinÿ the events that led to Darwin's theory of evolution. Therefore, first read the narrative to absorb thÿÿ big picture and then return to answer the few questions that accompany this material. 1. Define evolution broadly and then give a narrower definition, as discussed in the overview. This section takes a look at the historical setting and influences on Darwin, and it sets the stage fo,: our formal study of evolution.. How did each of the following sources view the origin of species? Aristotle and Scala Naturae The Old Testament CaroMs Linnaeus 3. Explain the role of fossils in rock strata as a window to life in earlier times. 4. How would Georges Cuvier have explained the appearance of the record of life shown in th rock strata?. James Hutton and Charles Lyell were geologists whose ideas strongly influenced Darwin ÿ thinking. What were the ideas each of them contributed? James Hutton Charles Lyell 6. What is the importance of the principle of uniformitarianism? 148 -
T Chapter 22: Descent with Modification: A Darwinian View of Life 7. Jean-Baptiste de Lamarck proposed a mechanism for how life changes over time. Explain the two principles of his mechanism. use and disuse inheritance of acquired characteristics 8. Although Lamarck's mechanism of evolution does not explain the changes in species over time, his thinking has been influential. What is considered to be the great importance of his ideas? 9. Charles Darwin proposed that the mechanism of evolution is natural selection and that it explains how adaptations arise. What are adaptations? Give two examples of them. 10. Explain the process of natural selection. 11. Let's try to summarize Darwin's observations that drive changes in species over time: d o 3 D O e-i Yÿ 1. Variations in traits exist. 2. These variations (traits) are heritable. 3. Species overproduce. 4. There is competition for resources; not all offspring survive. 12. From these four observations, what two inferences did Darwin make? 13. It is important to remember that differences in heritable traits can lead to differential reproductive success. This means that the individuals who have the necessary traits to promote survival in the current environment will leave the most offspring. How can this differential reproductive success affect the match between organisms and their environment? 14. To demonstrate your understanding of this section, complete the following sentences: do not evolve, evolve. 149 -
Chapter 22: Descent with Modification: A Darwinian View of Life Now, take out your highlighter and mark the information in the previous box. Hold these ideas firmly in your brain! Finally, if you are ever asked to explain Darwin's theory of evolution by natural selection (a common AP essay question), do not pull out the phrase "survival of the fittest." Instead, cite the points made in question 11 and explain the inferences that are drawn from them. 15. Use Figure 22.13 in your text to explain how research with soapberry bugs demonstrated observable evolutionary change. D i 16. MRSA is in the news today because it is becoming increasingly more common. What is it? 17. How did it become so dangerous? Explain the evolution of MRSA's resistance to methicillin. 18. Do antibiotics cause bacteria to become resistant? Explain your response. 19. Let's make a list of the four evidences for evolution that are described in this concept. Give an example of each. 150 -
Chapter 22: Descent with Modification: A Darwinian View of Life 20. How does the fossil record give evidence for evolution? 21. What is meant by each of the following terms? Give an example of each. 22. How do homologous structures give evidence for evolution? 23. What is summarized in an evolutionary tree? 24. Figure 22.17 in your text shows an evolutionary tree. What is indicated by each branch point in the following figure? Mark each branch point.? "i 0 25. What is indicated by the hatch marks in Figure 22.17? +,a ÿ,1 26. Use the tree in question 24 to answer this question: Are crocodiles more closely related to lizards or to birds? Explain your response. 27. On the evolutionary tree, label the vertical lines to the right, and annotate the key feature that marks each group. 28. Organisms that are only distantly related can resemble each other. Explain convergent evolution, and describe how analogous structures can arise. Y - 151
Chapter 22: Descent with Modification: A Darwinian View of Life 29. Convergent evolution might be summarized like this: Similar problem, similar solution. Can you give two examples of convergent evolution? Study Tip Homologous smÿctures show evidence of relatedness (whale fin, bat wing). Analogous structures are similar solutions to similar problems but do not indicate close relatedness (bird wing, butterfly wing). 30. What is biogeography? How is it affected by continental drift and the presence of endemic species? Let's wrap up all of these ideas with a final summary. OR GANIZE I70 UR THO UGHTS 1. Evolution is a change in a species over time. 2. Heritable variations exist within a population. 3. These variations can result in differential reproductive success. 4. Over generations, this can result in changes in the genetic composition of the population. And remember: Individuals do not evolve! Populations evolve. Test Your Understanding Answers Now you should be ready to test your knowledge. Place your answers here: 1. 2. 3. 4. 5. - 152 -
Chapter 23: The Evolution of Populations Name Period Chapter 23: The Evolution of Populations This chapter begins with the idea that we focused on as we closed the last chapter: Individuals do not evolve! Populations evolve. The overview looks at the work of Peter and Rosemary Grant with Galitpagos finches to illustrate this point, and the rest of the chapter examines the change in populations over time. As in the last chapter, first read each concept to get the big picture and then go back to work on the details presented by our questions. Don't lose sight of the conceptual understanding by getting lost in the details! 1. What is microevolution? 2. What are the three main mechanisms that can cause changes in allele frequency? 3. What is the only mechanism that is adaptive, or improves the match between organisms and their environment? Colÿeept 23.t ÿ5)ÿeÿic ÿ,ÿojatioÿ mÿdÿes eÿ,ofdÿtioga yossÿb{e d d 4. Because Darwin did not know about the work of Gregor Mendel, he could not explain how organisms pass heritable traits to their offspring. In looking at genetic variation, what are discrete characters, and what are quantitative characters? o 5. Using the techniques of molecular biology, what are the two ways of measuring genetic variation in a population?. Geographic variation may be shown in a graded manner along a geographic axis known as a cline. What external factors might produce a dine? Why does the existence of a cline suggest natural selection? 7. Several sources of genetic variation are available. What is the ultimate source of new alleles?. Mutations are any change in the nucleotide sequence of an organism's DNA. These mutations provide the raw material from which new traits may arise and be selected. What occurs in a point mutation? Why don't all point mutations result in a change of phenotype? 9. What is translocation? How can it be beneficial? - 153 -
Chapter 23: The Evolution of Populations 10. Chromosomal changes that delete, disrupt, or rearrange many loci at once are usually harmful. How does gene duplication occur? How might it play a role in evolution? 11. Much of the genetic variation that makes evolution possible comes through sexual reproduction. What are the three mechanisms by which sexual reproduction shuffles existing alleles? 12. What is apopulation? 13. What is a gene pool? 14. The greater the number of fixed alleles, the lower the species' diversity. What does it mean to say that an allele isfixed?. 15. The Hardy- Weinberg principle is used to describe a population that is not evolving. What does this principle state? 16. If the frequency of alleles in a population remains constant, the population is at Hardy Weinberg equilibrium. There are five conditions for Hardy-Weinberg equilibrium. It is very important for you to know these conditions, so enter the conditions on the left side of the chart and a brief explanation of the condition on the right side. CONDITIONS FOR HARDY-WE][NBERG EQUILIBRI[UM. 2. 3. 4. 5. It is not very likely that all five of these conditions will occur, is it? Allelic frequencies change. Populations evolve. This data can be tested by applying the Hardy-Weinberg equation. Let's look at how to do this. - 154 -
Chapter 23: The Evolution of Populations Eqÿaÿ.cÿ ÿbr Har@o;Wehÿerg Eqaÿbrÿm p2 + 2pq + q2 = I where p2 is equal to the frequency of the homozygous dominant in the population, 2pq is equal to the frequency of all the heterozygotes in the population, and q2 is equal to the frequency of the homozygous recessive in the population. Consider a gene locus that exists in two allelic forms, A and a, in a population. Let p = the frequency of A, the dominant allele and q = the frequency of a, the recessive allele. So, p2 = AA, q2 = aa, 2pq = Aa If we know the frequency of one of the alleles, we can calculate the frequency of the other allele: p+q= 1, so p=l-q q=l-p d d ==i d D /3 17. In a plant population, suppose that red flowers (R) are dominant to white flowers (r). In a population of 500 individuals, 25% show the recessive phenotype. How many individuals would you expect to be homozygous dominant and heterozygous for this trait? (A complete solution for this problem is at the end of this Reading Guide chapter.) 0 eq D O eq 18. In a population of plants, 64% exhibit the dominant flower color (red), and 36% of the plants have white flowers. What is the frequency of the dominant allele? (There are a couple of twists in this problem, so read and think carefully. A complete solution for this problem is at the end of this Reading Guide chapter.) Cÿ 155 -
Chapter 23: The Evolution of Populations 19. First, let's try to summarize the big idea from this section. Scan through the entire concept to pull out this information. Three major factors alter allelic frequency and bring about evolutionary change. List each factor, and give an explanation. 20. Which of the previous factors results in a random, nonadaptive change in allelic frequencies? 21. Which of the previous factors tends to reduce the genetic differences between populations and make populations more similar? 22. Of the three factors you previously listed, only one results in individuals that are better suited to their environment. Which is it? 23. Explain what happens in each of these examples of genetic drift: founder effect bottleneck effect 24. In evolutionary terms, fitness refers only to the ability to leave offspring and contribute to the gene pool of the next generation. It may have nothing to do with being big, or strong, or aggressive. Define relative fitness. 25. What is the relative fitness of a sterile mule? 156 -
Chapter 23: The Evolution of Populations 26. Figure 23.13 in your text is important because it helps explain the three modes of selection. Label each type of selection, and fill in the chart to explain what is occurring. [ "." -",, ii....j I Stabilizing Directional Disruptive i 27. What is often the result of sexual selection? 28. What is the difference between intrasexual selection and intersexual selection? Give an example of each type of selection. {} +.a a,ÿ 29. Explain two ways in which genetic variation is preserved in a population. 30. Discuss what is meant by heterozygote advantage, using sickle-cell anemia as an example 31. Give four reasons why natural selection cannot produce perfect organisms. 157 -
Chapter 23' The Evolution of Populations Test Your Understanding Answers Now you should be ready to test your knowledge. Place your answers here: 1. 2. 3. 4. 5. 6. Solution to Questioÿ 17 Let p = frequency of the dominant allele (R) and q = frequency of the recessive allele (r). 1. q2 = frequency of the homozygous recessive = 25% = 0.25. Since q2 = 0.25, q = 0.5. 2. Now, p+q= 1, sop=0.5. 3ÿ Homozygous dominant individuals are RR or p2 = 0.25, and they will represent (0.25)(500)= 125 individuals. 4. The heterozygous individuals are calculated from 2pq = (2)(0.5)(0.5) = 0.5, and in a population of 500 individuals will be (0.5)(500) = 251} individuals. Solution to Questiot7 18 This problem requires you to recognize that individuals with the dominant trait can be either homozygous or heterozygous. Therefore, you cannot simply take the square root of 0.64 to get p. For problems of this type, you must begin with the homozygous recessive group. So... Let p = frequency of the dominant allele (R) and q = frequency of the recessive allele (r). 1. q2 = frequency of the homozygous recessive = 36% = 0.36. Because q2 = 0.36, q = 0.6. 2ÿ 3. Now, p + q = 1, sop = 0.4. Notice that this problem asks for the frequency of the dominant allele (p), not the frequency of the homozygous dominant individuals (p2). So, you are done.., the frequency of the dominant allele = 40%. 158 -
Chapter 24: The Origin of Species Name Period Chapter 24: The Origin of Species 1. What was Darwin's "mystery of mysteries"? 2. Define speciation. 3. Distinguish between microevolution and macroevolution. Concept 24d 7Yÿe biological :ÿyecfes c(mces eÿgdmsi:ÿ:es rÿrodg, cff,,e fsod;ÿ fojÿ 4. Use the biological species concept to define species. 5. What is required for the formation of new species? 6. What are hybrids? d d 7. Explain the two types of barriers that maintain reproductive isolation. O, The following charts summarize the various ways that reproductive isolation is maintained. Explain and give an example of each type of isolating mechanism. o Habitat isolation eq Temporal isolation Behavioral isolation Mechanical isolation Gametic isolation? 2 159 -
Chapter 24: The Origin of Species Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown, The concept of reproductive isolation is essential for an understanding of speciation, so we are going to have you look at it again. Refer to Figure 24.3 in your text, and label the following sketch. Name each type of isolating mechanism............. "...,,...... '"... 'ÿ;'... ;b @ @ 160 -
Chapter 24: The Origin of Species Colÿeept 24.2 HOeciaAoÿ cÿm ÿke p&ce ÿ,h"}ÿ or n,ia}oÿd geogrÿgbmc s<bÿr'aaoÿ' 10. Gene flow can be interrupted in two main ways. Explain and give an example of each by labeling and annotating this figure, which shows an ancestral species of fish and then the two modes of speciation.,i / ÿ -, [ ' 3j :'IX, / 11. What type of speciation is caused by a barrier such as the Grand Canyon? 12. Sympatric speciation occurs in populations that live in the same geographic area. How is this possible? e,i @ 13. Your response to question 12 should have listed polyploidy, habitat differentiation, and sexual selection. These are not easy concepts to understand, so let's spend some time with each of them. To begin, use the following figure to explain autopolyploidy. /j....... \, o \\x / / 161
Chapter 24: The Origin of Species 14. Now, use this figure to explain allopolyploid speciation. 15. Before we leave allopatric and sympatric speciation, explain what happens in sexual selection, and how this process can drive sympatric speciation. Calmep 24,3 f<ÿ;bad ;;oÿes' proÿ,me <ÿbortÿmities go,ÿ'mdy f(ÿe ors t}}at eau,ve rÿ<gÿrod?ÿcth,e isolÿhoÿ ] 6. What are hybrid zones? Cotmept 24.4 5)ÿedatioÿ eÿ'm oeem rÿ Ndÿ), or sloÿ@ÿ, cmd # ealÿ res'ÿ# Ji'om ehÿt<ÿ<es #ÿ.ibÿ, or mayo, geÿes' 17. Stephen Jay Gould and Niles Eldredge coined the term punctuated equilibria. What is meant by a punctuated pattern? 18. Label this figure, and explain how each of the pictures explains speciation. Test Your Understanding Answers Now you should be ready to test your knowledge. Place your answers here: 1. 2. 3. 4. 5. 6, 7. - 162 -