Test Bank for Evolution Making Sense of Life 2nd Edition By Carl Zimmer

Test Bank, Chapter 3 1. Lord Kelvin argued that based on the temperature of rocks, the earth could not be as old some geologists thought. What turned out to be wrong with his reasoning? (a) he claimed that the temperature of surface rocks should be used in calcuations, but these calculations were shown to be unreliable (b) he did not realize that the planet’s interior was constantly changing (c) the upper layers of the earth are cooler than Kelvin realized (d) all of the above 2. Which of the following allowed scientists to determine whether early hominins were browsers (eating shrubs primarily) or grazers (eating grasses primarily)? (a) shrubs and grasses differ in the type of photosynthesis they perform (b) shrubs and grasses have different carbon isotopic signatures (c) fossil remains of plants surrounding hominins indicate what they most likely ate (d) a and b are correct (e) a, b, and c are correct 3. Scientists discover a new fossil that they expect is at least three million years old. To estimate the age of the fossil they would most likely: (a) search for layers of volcanic ash in rock layers above an below the location of the fossil (b) use radiocarbon dating to determine the age of the fossil itself (c) use radiocarbon dating to determine the age of the sedimentary layer in which the fossil was found (d) all of the above 4. Minik Rosing and Robert Frei have argued that life likely existed as far back as 3.7 billion years ago. They base this claim on: (a) the presence of biomarkers in rocks of that age (b) fossils of stromatolites in rocks of that age (c) fossils of photosynthetic bacteria in rocks of that age (d) the presence of tiny blobs of mineral-rich fluids in rocks of that age 5. The earliest generally accepted fossils of living organisms are: (a) yeasts (b) stromatolites (c) zircons (d) carbon isotopes 6. Eukaryotes differ from archaea and bacteria because: (a) they contain a nucleus (b) the cell membrane contains peptidoglycan (c) they contain mitochondria (d) a and c are correct (e) a, b, and c are correct 7. The transition of from single-celled to multi-celled organisms: (a) happened once (b) happened on multiple occasions (c) occurred before the origin of eukaryotes (d) a and c are correct (e) b and c are correct 8. The earliest animal fossils appear similar to modern day: (a) sponges (b) archaea (c) fungi (d) jellyfish 9. Tetrapods include: (a) organisms descended from ancestors with four limbs (b) birds (c) whales (d) all of the above 10. The Edicaran fauna includes: (a) organisms that lived on land (b) tetrapods (c) organisms that are not clearly related to any currently existing lineages (d) chordates 11. Nearly all currently existing animal lineages evolved during which period? (a) Ediacaran (b) Precambrian (c) Cambrian (d) Cryogenian 12. Prokaryotes include representatives from: (a) bacteria (b) archaea (c) eukarya (d) a and b (e) a, b, and c are all correct 13. The oldest currently known fossil of a land animal is: (a) a tetrapod (b) a bird (c) a millipede (d) bacteria 14. Modern day mammals are descended most recently from what group: (a) synapsids (b) reptiles (c) fish (d) amphibians 15. The diversification of grasses has occurred mostly in the last 20 million years. Some scientists have argued that this can be explained by: (a) the decline of large herbivores (b) the extinction of dinosaurs (c) a decline in the concentration of carbon dioxide in the atmosphere (d) the emergence of insects 16. The earliest fossils of our own species date to: (a) approximately 500,000 years ago (b) approximately, 2 million years ago (c) approximately 6 million years ago (d) approximately 200,000 years ago 17. What are four features shared by all chordates? 1. notochord 2. hollow nerve chord 3. pharyngeal gill slits as embryos 4. post anal tail as embryos 18. Imagine you discovered a fossil from an adult organism that you suspect might be an ancient chordate. What structure would you look for to confirm you suspicion? You could look for the presence of a notochord. Structures such as the pharyngeal gill slits and post anal tail may only be seen in embryos. 19. Give one explanation that has been proposed for why grasses expanded and diversified around 20 million years ago. Around this time the level of carbon dioxide in the atmosphere began to decline. Grasses perform C4 photosynthesis and are therefore more efficient at extracting carbon dioxide from the atmosphere than C3 plants. 20. Match the following species or taxonomic groups with the approximate time period in which they appear in the fossil record: Bacteria 3.5 bya Mammals 150-200 mya Tetrapods 370 mya Flowering plants 132 mya Sponges 650 mya 21. What factor might scientists take into account when choosing an isotope to date a new fossil. The scientists would need to consider how old the fossil may be relative to the length of the half-life of different radioactive isotopes. Isotopes with a longer half-life will be better for older fossils, while isotopes with a shorter half-life will be better for younger fossils. 22. Describe one advantage that carbon dating provides over other types of radiometric dating. Dating with other radioisotopes only allows scientists to date rocks. Thus, the approximate age of fossils has to be estimated based on dates for adjacent layers of volcanic ash. Carbon dating can be performed on fossils or artifacts themselves, as long as they are not older than about 40,000 years. 23. Explain how carbon isotopic signatures can be used to determine diets of extinct organisms. Plants obtain carbon from the atmosphere, which is a mixture of different isotopes (C-13 and C-14). The carbon becomes incorporated into plant biomass. Different plants have different carbon isotopic signatures depending on how they perform photosynthesis. For example, C4 plants have lower levels of carbon -13 than C3 plants. The ratio of carbon isotopes in animals reflects their diet. For example, animals that graze primarily on grass would be expected to have less carbon-13 because grasses are C4 plants. By examining the carbon isotopic signature of fossils extinct organisms, and comparing them to signatures found in organisms with a known diet, scientists can get some idea about the diet of the extinct animal. 24. Describe an example of where fossils have been used to reconstruct the behavior of extinct animals. 1. Fossils of ichthyosaurs show some females pregnant, indicating that they gave live birth. 2. Fossils have been discovered that show one organism in the process of eating another, thus giving an indication of diet. 3. Fossilized trackways of sauropod dinosaurs indicate migratory patterns and group composition. 4. Fossils of eggs, hatchlings, and adults demonstrate that some dinosaurs practiced parental care. 25. Describe three reasons why any given organism would be unlikely to be discovered in fossilized form. 1. Most organisms are eaten or otherwise degraded to the point where there is nothing left to fossilize. 2. Fossilization typically requires organisms to be in water and rapidly covered with sediment. 3. Soft-bodied organisms are unlikely to fossilize. 4. A fossil must rise to the surface of the earth. 5. A fossil may be destroyed by erosion 6. A fossil must be discovered. Test bank, Chapter 6 1. Tasmanian devils once inhabited most of present day Australia, but only an isolated population on the island of Tasmania has survived to present day. Which of the following processes has likely affected Tasmanian devils as a result of this history: (a) a higher mutation rate (b) stronger natural selection (c) a genetic bottleneck (d) gene flow 2. The effectiveness of selection on an allele depends in part on: (a) the frequency of the allele (b) the magnitude of average excess fitness (c) the average fitness of the population (d) all of the above (e) none of the above 3. Inbreeding: (a) increases heterozygosity in populations (b) creates deleterious recessive alleles (c) increases homozygosity in populations (d) all are correct (e) b and c are correct 4. Genetic drift: (a) will always lead to higher fitness of individuals in the population (b) reduces genetic variation within a population (c) can lead to divergence between populations (d) b and c are correct (e) a, b, and c are correct 5. In a population of infinite size, which statement accurately describes the eventual fate of a new beneficial allele? (a) If it is dominant, it will reach fixation; if it is recessive it will rise to high frequency but not reach fixation (b) If it is dominant it will rise to high frequency but will not reach fixation; if it is recessive it will reach fixation (c) Since it is advantageous, it will reach fixation regardless of whether it is dominant or recessive (d) Regardless of whether it is dominant or recessive, it will rise to high frequency but not reach fixation 6. Lively and Dybdahl studied parasite infection rates in a population of asexual clonal snails. The graph above shows relative infection rates for the four most common clone genotypes and for several rare genotypes (all lumped together). Based on these data they hypothesized that parasites adapted to infecting the most common clone genotypes in the population, and thus these genotypes had lower fitness. This is consistent with ________operating in the population. Further evidence would be provided if: (a) genetic drift; heterozygosity declined over time in the population (b) genetic drift; rare clones were lost from the population frequency-dependent selection; (c) negative frequency-dependent selection; rare clones became common in the next generation, but then declined in frequency in the following generation (d) negative frequency-dependent selection; rare clones became more common until they completely replaced the clones that were originally common 7. Assuming that a deleterious allele is maintained in a population by mutation-selection balance, which scenario below describes the case where you would expect the equilibrium frequency of the allele to be highest? (a) the mutation rate is low; the allele is highly deleterious (b) the mutation rate is low; the allele is slightly deleterious (c) the mutation rate is high; the allele is highly deleterious (d) the mutation rate is high; the allele is slightly deleterious 8. Inbreeding results in a higher frequency of ________ in a population. Inbreeding depression occurs because _______. (a) deleterious alleles; individuals with deleterious alleles have high mortality (b) heterozygosity; heterozygotes have lower fitness (c) homozygosity; deleterious recessive alleles are expressed more often (d) heterozygosity; deleterious dominant alleles are expressed more often 9. Below you see graphs that depict the change in frequency of a neutral allele in four populations that differ in size. Which population would you predict is the smallest? Answer: D 10. The frequency of a slightly deleterious allele maintained at an equilibrium frequency by mutation-selection balance would be higher: (a) if the mutation rate is high (b) if the mutation rate is low (c) if the selection coefficient is high (d) if the population size is small 11. Genetic drift: (a) reduces genetic variation within a population (b) increases divergence (variation) between populations (c) affects only neutral alleles (d) a and b are correct (e) a, b, and c are correct 12. Many plant species are hermaphroditic and run the risk of self-mating. Some species carry self-incompatibility alleles that can prevent this from occurring. If a pollen grain with self-incompatibility allele S1 lands on a stigma that also carries the S1 allele the pollen will not germinate and fertilization does not occur. Thus, this mechanism not only prevents selfing, but also has the unfortunate effect of preventing mating with any other plant that carries the same allele. However, if the pollen lands on a stigma of a plant with a different allele, fertilization occurs. Imagine a population of plants in which the allele frequency of S1=0.9 and the allele frequency of S2=0.1. All other things being equal, individuals with the ____ allele will have higher fitness on average. This is an example of______. (a) S1; positive selection (b) S2; positive selection (c) S1; negative frequency-dependent selection (d) S2; negative frequency-dependent selection 13. You collect the following data on genotypes for a sunflower population: AA: 40, AB: 20, BB: 40. Based on Hardy-Weinberg predictions you expected the following numbers: AA: 25, AB: 50, BB: 25. Which of the following is a plausible explanation for the deviation? (a) Balancing selection (b) Negative frequency-dependent selection (c) Inbreeding (d) Genetic drift 14. Some Drosophila melanogaster larvae use a “sitting” foraging strategy in which they feed more or less in the same location, while “rovers” wander around the substrate looking for more food sources. In the graph above, the red line corresponds to sitters and the purple line corresponds to rovers. This is an example of _______; over time we expect________: (a) Negative frequency-dependent selection; both strategies to persist in the population (b) pleiotropy; both strategies to persist in the population (c) frequency-dependent selection; the rover strategy to replace the sitter strategy because it has the highest fitness (d) pleiotropy; the rover strategy to replace the sitter strategy because it has the highest fitness 15. Mutations in the GDF9 gene in sheep have been linked to changes in female fecundity. The following are the relative fitnesses of different genotypes in the population: Relative fitness +/ - 1 +/ + 0.7 -/ - 0.1 (a) this is an example heterozygote advantage; genetic variation will be maintained over time (b) this is an example of negative frequency-dependent selection; genetic variation will be maintained over time (c) this is an example of heterozygote advantage; genetic variation will be lost over time (d) this is an example of negative frequency-dependent selection; genetic variation will be lost over time 16. The graph above shows the change in allele frequency for a beneficial allele over time (x-axis shows generations). Based on the shape of the curve this allele is most likely: (a) homozygous (b) dominant (c) recessive (d) heterozygous (e) additive 17. Considering the principles of mutation, natural selection, and genetic drift do you expect adaptive evolution to occur more rapidly in small or large populations? What about non adaptive evolution? For each answer, please explain your reasoning. Adaptive evolution will occur more rapidly in a large population. Adaptation occurs through the process of natural selection, which is more effective in large populations because there are more mutations (some may be beneficial) and the effects of random genetic drift are relatively weak compared to a small population. Non-adaptive evolution would be more likely in a small population because genetic drift is stronger. Genetic drift is the result of random sampling error, without regard to the fitness effects of alleles. Thus, in a small population, slightly deleterious alleles may be fixed by drift. 18. You are studying a population of 100 flowers that has two alleles at a locus for flower color, blue (B) and green (G). There are 15 individuals with the BB genotype, 70 individuals with the BG genotype, and 15 individuals with the GG genotype. (a) (6 pts) What are the allele frequencies of B and G in the starting population? Show your calculations. Freq B= 15 x 2 +70 = 100/200=0.5 Freq G= 15 x 2 +70 = 100/200=0.5 (b) (5 pts) Is this population in Hardy-Weinberg equilibrium? Show your calculations. Expected genotype frequencies from HW equation: BB = 0.52 = 0.25 GG = 0.52 = 0.25 BG = 2 x 0.5 x 0.5 = 0.5 Actual genotype frequencies: BB= 15/100 = 0.15 GG = 15/100 = 0.15 BG = 70/100 = 0.7 No, the population is not in HW equilibrium because expectations are not met. (c) (3 pts) Given the results of part b and the distribution of genotypes, offer a hypothesis that could explain the results—explain your reasoning. There is an excess of heterozygotes, which could be explained by heterozygote advantage. 19. Discuss the effectiveness of genetic drift and natural selection in small vs. large populations. Please be sure to explain why each process is stronger/weaker depending on the population size. Natural selection is stronger in a large population because there are more mutations, some of which may be beneficial. Moreover, because drift is weak in large populations selection is more likely to overcome the random loss of new beneficial mutations. Natural selection is weaker in small populations because there are fewer mutations, and the random effects of drift are likely to overpower selection in determining the fate of an allele. Drift is stronger is small populations because it results from random sampling error, which is more prominent in a small population. Sampling error is reduced in a large population, making drift relatively weaker. 20. Please describe two factors that would increase the likelihood of fixing a beneficial allele in a population of finite size. 1. A higher starting frequency means an allele is less likely to be lost by drift and more likely to be fixed by selection. 2. A larger excess fitness means selection for the allele will be stronger and it will be more likely to fix. 3. The larger the population size the more likely the allele will fix by selection. Drift will be weaker in a large population meaning that the beneficial allele is less likely to be lost by drift. 21. (6 pts) A researcher performs an experiment on fruit flies to monitor the change in allele frequency of an allele called “A.” She starts with 24 populations, each with an initial starting frequency for A of 0.5. Flies are maintained for 10 generations by transferring the offspring from each generation to a new vial, where they produce the next generation. For half of the populations she randomly selects 20 flies to transfer, while for the other half she randomly selects 200 flies to transfer. After 10 generations she collects the following allele frequency data: Treatment 1: 0.55, 0.6, 0.2, 0.9, 0.45, 0.35, 0.1, 0.65, 0.65. 0.55, 0.75, 0.35, Treatment 2: 0.85, 0.8, 0.75, 0.8, 0.75, 1.0, 0.8, 0.85, 0.9, 0.8, 0.85, 0.8 What is a plausible explanation for the differences between the treatments? Please make sure to explain your logic. Considering the fact that the allele increased in frequency in all replicates of treatment two, we can assume this allele is beneficial. In treatment one, even though the allele is beneficial it increases in some replicates but not in others. This discrepancy can be explained by the fact that treatment one had a smaller population size transferred each generation. As a result, drift was strong and, since it is a random process, the allele frequency fluctuated more or less randomly. 22. The graph above depicts the change in frequency for an advantageous allele in two different populations, both of infinite size. The strength of selection is the same in both populations. (a) What type of allele is this? Explain how you know. This is a recessive allele. You can tell by the shape of curve. Beneficial recessive alleles at low frequency are rarely present in the homozygous recessive genotype, which is the only genotype that has the advantageous phenotype. As a result, low frequency beneficial recessives rise very slowly in frequency until they become more common. This is clearly the case in both simulations above. (b) Why does the frequency of the allele in one of the populations rise faster than the frequency in the other population? The starting frequency is higher in the one that rises faster. (c) If given enough time, will the allele become fixed in each of these populations? Yes, in both cases the allele will be fixed by natural selection. In this case, the dominant allele is deleterious and can be eliminated by selection because the heterozygote expresses the dominant phenotype. 23. (a) Contrast evolution by natural selection with evolution by genetic drift? Evolution by natural selection is non-random and adaptive, while evolution by genetic drift is random and non-adaptive. 24. The earth’s biotic and abiotic environments are changing rapidly due, in part, to human activities. For example, the introduction of non-native invasive species into new habitats and climate change highlight two ways in which humans are altering the environment experienced by other species. Some species will probably adapt to these changes while others may not. Considering the processes of mutation, natural selection, and genetic drift comment on the likelihood of adaptation to environmental change for species that have small population sizes vs. species with large population sizes. At a minimum, a fully correct answer will incorporate all three of these processes into the answer. Large populations are more likely to adapt than small populations. In large populations, there will be more mutations, increasing the chances for a beneficial mutation to occur. Natural selection (which results in adaptation) will be more effective not only because there are more beneficial mutations, but also because the random effects of drift are weak in a large population. This means that new beneficial mutations are less likely to be lost by drift—even slightly beneficial mutations can be fixed by selection. The converse is true in small populations. There will be a smaller number of new mutations, and genetic drift, which is random and non-adaptive, will overpower natural selection. 25. (a) The graphs above show the results of simulations of the effect or selection on deleterious alleles. Population size is infinite in both simulations and the starting frequency and the strength of selection are the same. Based on the shape of the curves, why do the results of the simulations differ? Explain your answer. In the top simulation the deleterious allele is dominant. You can tell because the frequency drops rapidly, and the allele is completely eliminated by the end. A deleterious dominant can be eliminated because it will be expressed in the heterozygous genotype, meaning that the last copy of the allele in the population is visible to selection. In the bottom simulation the deleterious allele is recessive. You can tell because the rate of frequency decline decelerates as the frequency drops and the allele is not fully eliminated by the end. This happens because when deleterious recessive alleles are rare, they are most often found in heterozygotes, where the allele is not visible to selection because heterozygotes display the dominant phenotype. (b) The allele in the bottom simulation is not eliminated entirely from the population. Would this change if the population was finite in size? Why or why not? Yes, it would most likely be eliminated. Selection would bring the allele down to low frequency. Since the population is finite drift would also have an effect, and would most likely eliminate the allele (low frequency alleles are likely to be lost by drift). 26. The graph above shows results of two simulations, both depicting the rise in frequency of beneficial allele in a population of infinite size. The selection coefficient and the starting frequency are the same, but in one simulation the beneficial allele is dominant and in the other it is recessive. Neither allele is fixed by 500 generations. (a) Which simulation shows results for a dominant and which shows results for a recessive allele? How can you tell? The allele in simulation one is dominant and the allele in simulation two is recessive. You can tell because dominant alleles will rise in frequency more rapidly because the advantageous allele will be expressed in homozygotes and heterozygotes. Recessive alleles will rise slowly in frequency at first because the allele is only expressed in homozygotes. When the allele is rare, it will most likely be present in heterozygotes. (b) Neither of the alleles reaches fixation by 500 generations. If given enough time, will both of these alleles reach fixation in the population? Why or why not? The dominant allele will not reach fixation because the deleterious recessive allele cannot be eliminated by selection alone because it can “hide” from selection in the heterozygous genotype. The recessive allele will reach fixation because the deleterious dominant can be eliminated by selection because the allele is visible to selection in heterozygotes. 27. The graph above depicts the rise in resistance to warfarin in a rat population. Notice that after reaching a peak of 100% resistance, resistance in the population declined. Please provide a plausible evolutionary explanation for this. Genes conferring resistance to warfarin appear to have pleiotropic effects, resulting in a trade-off. When selection pressure from poisoning is present resistant individuals have the highest fitness. When the poisoning program ceased, this selection pressure was removed and non-resistant individuals had the highest fitness.