Test Bank for How Humans Evolved 7th Edition by Robert Boyd, Joan Silk All Chapters 1-15

Test Bank for How Humans Evolved 7th Edition by Robert Boyd, Joan Silk All Chapters 1-15 Test Bank for How Humans Evolved 7e by Robert Boyd, Joan Silk CHAPTER 1: Adaptation by Natural Selection MULTIPLE CHOICE 1. Adaptations are defined as the components of an organism that a. allow it to survive and reproduce. c. occur by random chance alone. b. allow it to evolve more rapidly. d. absolutely never change. ANS: A DIF: Medium REF: Explaining Adaptation Before Darwin OBJ: Describe why our modern understanding of the diversity of life is based on the ideas of Charles Darwin. MSC: Remembering 2. Which of the following is an adaptation? a. The human eye. b. Design by a divine creator. c. Both the human and the fish eye, but humans are better adapted to their environments than fish are to theirs. d. The Grand Canyon. ANS: A DIF: Easy REF: Explaining Adaptation Before Darwin OBJ: Explain how natural selection can produce very complex adaptations like the human eye. MSC: Applying 3. Influential nineteenth-century scientists like Charles Darwin concluded that the complex adaptations we see in plants and animals are problematic and require a special explanation because a. a divine creator designed them. b. it is very unlikely that they arose by random chance alone. c. they occur in most plants and animals. d. they have no real function. ANS: B DIF: Easy REF: Explaining Adaptation Before Darwin OBJ: Describe why our modern understanding of the diversity of life is based on the ideas of Charles Darwin. MSC: Understanding 4. Before Charles Darwin proposed his theory of natural selection by adaptation, many scholars argued that adaptations are proof that a. evolution is a process based on random chance alone. b. because of their ability to adapt quickly, humans are better than all other species. c. God exists and designs all things to fit a specific purpose. d. there is no way that God can exist. ANS: C DIF: Easy REF: Explaining Adaptation Before Darwin OBJ: Describe why our modern understanding of the diversity of life is based on the ideas of Charles Darwin. MSC: Remembering 5. Charles Darwin is known for his revolutionary argument that a. plants and animals are not designed by God and do not change over time. b. plants and animals change slowly over time. c. fossil plants and animals changed, but existing plants and animals do not. d. plants and animals are created by chance and then evolve through divine intervention. ANS: B DIF: Easy REF: Darwin’s Theory of Adaptation OBJ: Describe why our modern understanding of the diversity of life is based on the ideas of Charles Darwin. MSC: Remembering 6. The postulates that make up Darwin’s theory of adaptation include all of the following EXCEPT a. any given environment can support only a certain number of individuals. b. variation affects the ability of individuals to survive and reproduce. c. individuals always compete with each other physically. d. variation is passed from parents to offspring. ANS: C DIF: Easy REF: Darwin’s Theory of Adaptation OBJ: Describe why our modern understanding of the diversity of life is based on the ideas of Charles Darwin. MSC: Remembering 7. For natural selection to occur, variation must exist. This is true because without variation a. there is no way for change to occur between generations. b. the one trait that exists is always advantageous, and change is not necessary. c. there is no competition among individuals. d. traits are never inherited by offspring. ANS: A DIF: Hard REF: Darwin’s Theory of Adaptation OBJ: Explain how competition, variation, and heritability lead to evolution by natural selection. MSC: Understanding 8. Even though natural selection was named after the artificial selection that plant and animal breeders use, it really refers to a. the survival of the physically fit. b. the reproduction of traits from generation to generation. c. the selective retention of variation in a population. d. the variable ability of species to survive and reproduce. ANS: C DIF: Hard REF: Darwin’s Theory of Adaptation OBJ: Explain how competition, variation, and heritability lead to evolution by natural selection. MSC: Understanding 9. During 1976 on the Galápagos Island of Daphne Major, Peter and Rosemary Grant found evidence of natural selection by adaptation when they observed that a. finches with shallow beaks were less likely to survive and reproduce than finches with deep beaks. b. finch beak size had no effect on survival rates. c. many more small seeds were available for the finches to eat. d. more finches with deep beaks died than finches with shallow beaks. ANS: A DIF: Medium REF: Darwin’s Theory of Adaptation OBJ: See why natural selection sometimes causes species to become better adapted to their environments. MSC: Applying 10. Natural selection acted on the medium ground finch on Daphne Major because a. birds with medium beak sizes experienced higher mortality. b. a drought changed the environment where the finches lived. c. offspring of finches with small beaks did not survive the juvenile period. d. the population reached equilibrium. ANS: B DIF: Medium REF: Darwin’s Theory of Adaptation OBJ: See why natural selection sometimes causes species to become better adapted to their environments. MSC: Applying 11. Which of the following is an example of directional selection? a. Both small and large individuals survive. b. Only large individuals survive. c. The proportion of small and large individuals remains the same. d. Neither small nor large individuals survive. ANS: B DIF: Easy REF: Darwin’s Theory of Adaptation OBJ: Understand why natural selection can produce change or cause species to remain the same over time. MSC: Applying 12. Which of the following is an example of stabilizing selection? a. Both small and large individuals survive, but medium individuals die off. b. Only large individuals survive. c. The proportion of small and large individuals remains the same. d. Neither small nor large individuals survive. ANS: D DIF: Easy REF: Darwin’s Theory of Adaptation OBJ: Understand why natural selection can produce change or cause species to remain the same over time. MSC: Applying 13. When the Daphne Major finches reach a point where the costs of a having beak larger than average size outweigh the benefits, beak size will begin to stay the same, and the population will achieve a(n) ________ state. a. direction c. equilibrium b. trend d. drift ANS: C DIF: Easy REF: Darwin’s Theory of Adaptation OBJ: Understand why natural selection can produce change or cause species to remain the same over time. MSC: Remembering 14. If a population is in stasis (an unchanging state), then a. the population is in its natural state. b. natural selection is not acting on the population. c. the most common type of individual is consistently favored by stabilizing selection. d. the most common type of individual is consistently favored by disruptive selection. ANS: C DIF: Medium REF: Darwin’s Theory of Adaptation OBJ: Understand why natural selection can produce change or cause species to remain the same over time. MSC: Understanding 15. After a drought, a scientist collects dead birds and finds that most of the individuals that did not survive to adulthood have either small or large beaks. Given this pattern, how would you expect selection to act on the population? a. Selection will not change the mean beak size. b. Selection will make the mean beak size in the population smaller. c. Selection will make the mean beak size in the population larger. d. The entire population will die out. ANS: A DIF: Medium REF: Darwin’s Theory of Adaptation OBJ: Understand why natural selection can produce change or cause species to remain the same over time. MSC: Analyzing 16. Species are best described as populations of organisms that a. are best adapted to their environment. b. assume some fixed characteristics. c. are dynamic. d. cannot be modified or go extinct. ANS: C DIF: Medium REF: Darwin’s Theory of Adaptation OBJ: See why natural selection usually works at the level of the individual but not at the level of the group or species. MSC: Understanding 17. Natural selection usually acts upon and produces adaptations at the level of the a. gene. c. group. b. individual. d. species. ANS: B DIF: Easy REF: Darwin’s Theory of Adaptation OBJ: See why natural selection usually works at the level of the individual but not at the level of the group or species. MSC: Remembering 18. Natural selection generally produces adaptations that are a. harmful to both individuals and groups. b. helpful to individuals but harmful to groups. c. harmful to individuals but helpful to groups. d. not successful unless every member of the group survives and reproduces. ANS: B DIF: Medium REF: Darwin’s Theory of Adaptation OBJ: See why natural selection usually works at the level of the individual but not at the level of the group or species. MSC: Understanding 19. Fecundity is defined as the ability of a. a population to have variation. b. an individual to compete for resources. c. an individual to survive to adulthood. d. an individual to produce offspring. ANS: D DIF: Easy REF: Darwin’s Theory of Adaptation OBJ: See why natural selection usually works at the level of the individual but not at the level of the group or species. MSC: Remembering 20. When all females have high fecundity, a population can be driven to extinction. This occurs because of a. natural selection. c. blending inheritance. b. convergence. d. continuous variation. ANS: A DIF: Medium REF: Darwin’s Theory of Adaptation OBJ: See why natural selection usually works at the level of the individual but not at the level of the group or species. MSC: Applying 21. Despite its detrimental nature, cannibalism can evolve by natural selection because a. cannibalistic groups are ferocious enough to scare predators away. b. individuals who cannibalize have higher fitness than those who do not. c. natural selection is always immoral. d. cannibalistic individuals kill off the rest of their population and have no mates left to reproduce with. ANS: B DIF: Medium REF: Darwin’s Theory of Adaptation OBJ: See why natural selection usually works at the level of the individual but not at the level of the group or species. MSC: Analyzing 22. Continuous variation occurs when a. no real variation is apparent between forms. b. variants come in distinct forms. c. variants come in a smooth distribution from one extreme to another. d. only one extreme variant exists. ANS: C DIF: Easy REF: The Evolution of Complex Adaptations OBJ: Explain how natural selection can produce very complex adaptations like the human eye. MSC: Remembering 23. Discontinuous variation occurs when a. no real variation is apparent between forms. b. variants come in distinct forms. c. variants come in a smooth distribution from one extreme to another. d. only one extreme variant exists. ANS: B DIF: Easy REF: The Evolution of Complex Adaptations OBJ: Explain how natural selection can produce very complex adaptations like the human eye. MSC: Remembering 24. Achondroplasia is a genetic adaptation that causes affected individuals to be much shorter than other people. This adaptation is an example of a. convergence. c. discontinuous variation. b. gene flow. d. outbreeding. ANS: C DIF: Easy REF: The Evolution of Complex Adaptations OBJ: Explain how natural selection can produce very complex adaptations like the human eye. MSC: Remembering 25. Many of Darwin’s contemporaries argued that discontinuous variation is the reason that complex traits evolve. However, Darwin reasoned that discontinuous traits do not play a major role because evolution a. happens only in large leaps. c. occurs very rapidly. b. occurs by singular, chance events. d. is a gradual process. ANS: D DIF: Medium REF: The Evolution of Complex Adaptations OBJ: Explain how natural selection can produce very complex adaptations like the human eye. MSC: Understanding 26. Discontinuous variation is unlikely to lead to new species because a. quick changes are never found in the fossil record. b. complex adaptations are unlikely to occur in a single jump. c. selection cannot act on discontinuous variation. d. it allows for only small incremental changes. ANS: B DIF: Medium REF: The Evolution of Complex Adaptations OBJ: Explain how natural selection can produce very complex adaptations like the human eye. MSC: Understanding 27. Darwin believed that when a new species arises, it does so by a. immediately achieving a distinct, discontinuous form. b. achieving perfection through natural selection in the first try. c. gradually accumulating small changes. d. following God’s will. ANS: C DIF: Medium REF: The Evolution of Complex Adaptations OBJ: Explain how natural selection can produce very complex adaptations like the human eye. MSC: Understanding 28. How do complex adaptations usually evolve? a. By a single large step due to a highly adaptive mutation b. By many small steps, but only when each is an improvement over the last step c. By many small steps, but only when each has a minimal effect on fitness d. By single large steps, but only when natural selection is strong ANS: B DIF: Medium REF: The Evolution of Complex Adaptations OBJ: Explain how natural selection can produce very complex adaptations like the human eye. MSC: Understanding 29. Which of the following was likely the first adaptation to occur during the evolution of the human eye? a. A protective cover and internal structures b. A depression where information about light and light movement is collected c. A simple, light-sensitive photo receptor d. Neural machinery for image processing ANS: C DIF: Hard REF: The Evolution of Complex Adaptations OBJ: Explain how natural selection can produce very complex adaptations like the human eye. MSC: Analyzing 30. A complex adaptation like the human eye exists in its present form because a. past organisms evolved and utilized a transitional form of the modern eye. b. extreme forms of variation allowed it to evolve in a single jump. c. it was created by a chance mutation. d. many organisms have eyes. ANS: A DIF: Easy REF: The Evolution of Complex Adaptations OBJ: Explain how natural selection can produce very complex adaptations like the human eye. MSC: Applying 31. Convergent evolution occurs a. when all members of a species become more similar. b. as a result of stabilizing selection. c. when natural selection produces similar adaptations in unrelated species. d. when individuals have equal fitness. ANS: C DIF: Medium REF: The Evolution of Complex Adaptations OBJ: Explain how natural selection can produce very complex adaptations like the human eye. MSC: Remembering 32. Convergent evolution provides evidence that complex adaptations are not a matter of mere coincidence because a. evolution always occurs in very different ways. b. the same process of evolution can occur independently in unrelated species. c. the process of evolution is biologically determined and not flexible. d. no two species ever end up with similar traits. ANS: B DIF: Easy REF: The Evolution of Complex Adaptations OBJ: Explain how natural selection can produce very complex adaptations like the human eye. MSC: Understanding 33. The morphology of the marsupial wolf of Tasmania is very similar to that of the placental wolves of Eurasia. This is an example of a. blending inheritance. c. essentialism. b. convergent evolution. d. continuous variation. ANS: B DIF: Medium REF: The Evolution of Complex Adaptations OBJ: Explain how natural selection can produce very complex adaptations like the human eye. MSC: Applying 34. A South American marsupial cat and a North American placental cat existed 10,000 years ago and shared a tree shrew-like common ancestor about 120 million years before that. Both of these animals evolved a saber-toothed adaptation. What does the presence of this complex trait mean? a. Tree shrews have saber teeth. b. The same complex adaptation evolved twice independently. c. Saber teeth are very common. d. North American and South American cat populations were interbreeding. ANS: B DIF: Hard REF: The Evolution of Complex Adaptations OBJ: Explain how natural selection can produce very complex adaptations like the human eye. MSC: Analyzing 35. How fast does evolution by natural selection take place? a. It is such a slow process that a single adaptation requires millions of years. b. It is so slow that it cannot be seen in the fossil record. c. It is fast enough that several new species can evolve from other forms in a few million years. d. It is so rapid that new species often evolve in a matter of decades. ANS: C DIF: Medium REF: Rates of Evolutionary Change OBJ: Explain how natural selection can produce very complex adaptations like the human eye. MSC: Understanding 36. Using the rate of change that the Grants observed in the medium ground finch, and assuming a selection event only occurs once every century, how rapidly would you predict that a species of finch like the large ground finch could evolve? a. It would take millions of years for only beak size to evolve. b. The medium ground finch could evolve into the large ground finch in 20 years. c. Natural selection could produce a new species of ground finch in a few thousand years. d. Because selection generally pushes constantly in one direction, a new species of ground finch could evolve in a single century. ANS: C DIF: Hard REF: Rates of Evolutionary Change OBJ: Explain how natural selection can produce very complex adaptations like the human eye. MSC: Applying 37. What does the Grants’ study of medium ground finches tell us about evolution by means of natural selection? a. New species cannot form. b. A new species can form only when natural selection operates consistently in one direction for a few million years. c. Evolution can change only single traits within a species. d. New species normally take thousands to millions of years to arise because natural selection pressures operate in fits and starts. ANS: D DIF: Medium REF: Rates of Evolutionary Change OBJ: Explain how natural selection can produce very complex adaptations like the human eye. MSC: Understanding 38. In order for the medium ground finch to evolve into the large ground finch over a 46-year period, what environmental scenario would have to occur? a. No selective pressure from the environment b. Constant selective pressure from the environment c. An isolated fit of extreme selective pressure from the environment followed by no selective pressure at all d. Constantly changing selective pressure from the environment ANS: B DIF: Medium REF: Rates of Evolutionary Change OBJ: Explain how natural selection can produce very complex adaptations like the human eye. MSC: Analyzing 39. What is unique about evolution by means of artificial selection (for example, domestic dogs)? a. It takes longer because there is no selection pressure. b. Stabilizing selection commonly occurs. c. Selection pressure occurs in fits and starts. d. It can occur rapidly because selection pressure is constant. ANS: D DIF: Easy REF: Rates of Evolutionary Change OBJ: Explain how natural selection can produce very complex adaptations like the human eye. MSC: Understanding 40. Which of the following is NOT an example of how selection is able to produce complex evolutionary changes in remarkably short periods of time? a. Using artificial selection, people intentionally created dozens of different forms of domesticated pigeons in just a few hundred years. b. A study of fish from the genus Poeciliopsis shows that short generation times allowed three different types of placenta to evolve in less than 2.4 million years. c. Theoretical studies of the evolution of the eye in an aquatic organism show that because of a short generation time, a complex eye could evolve in less than a million years. d. The fossil record indicates that the human brain took 2 million years to double in size. ANS: D DIF: Medium REF: Rates of Evolutionary Change OBJ: Explain how natural selection can produce very complex adaptations like the human eye. MSC: Applying 41. Theoretical studies of the evolution of the eye revealed that a. approximately 1,800 incremental changes of 1% could allow the eye to evolve from a single photo receptor to a spherical gradient lens. b. it would take more than 10 million years for the eye to evolve in an aquatic species with a short generation time. c. it was built by artificial selection in no more than 500 years. d. after 1,800 changes, an eye would still be in the photo receptor phase. ANS: A DIF: Hard REF: Rates of Evolutionary Change OBJ: Explain how natural selection can produce very complex adaptations like the human eye. MSC: Remembering 42. One of the things that Darwin had difficulty explaining was how inheritance worked. Why was inheritance so difficult for Darwin? a. The prevailing theory of inheritance was based on random mating. b. The prevailing theory of inheritance was incompatible with the maintenance of variation. c. The prevailing theory of inheritance implied that variation was not inherited from parents. d. The prevailing theory of inheritance implied that too much variation exists for natural selection to operate. ANS: B DIF: Easy REF: Darwin’s Difficulties Explaining Variation OBJ: Explain how competition, variation, and heritability lead to evolution by natural selection. MSC: Understanding 43. Which of the following is an example of blending inheritance? a. A tall individual marries a short individual, and all of their offspring are intermediate in height. b. All of the domestic breeds of dogs that are alive today are descended from a wolf ancestor. c. Offspring from two unrelated species of cats have similar saber-toothed adaptations. d. A red-headed individual marries an individual with black hair, and all of their offspring have black hair. ANS: A DIF: Medium REF: Darwin’s Difficulties Explaining Variation OBJ: Explain how competition, variation, and heritability lead to evolution by natural selection. MSC: Applying 44. Darwin could not convince his contemporaries of natural selection because a. Darwin thought that discontinuous variation was important for evolution. b. they believed in genetic inheritance. c. Darwin believed in blending inheritance, which reduces variation. d. they believed that traits were inherited from only one parent. ANS: C DIF: Medium REF: Darwin’s Difficulties Explaining Variation OBJ: Explain how competition, variation, and heritability lead to evolution by natural selection. MSC: Remembering 45. Which of the following provides an example of why Jenkin called Darwin’s ideas incompatible? a. Tall and short individuals are not able to breed with one another because they look different. b. If tall and short individuals breed with one another, all of their offspring will be short, and variation will disappear. c. If tall and short individuals breed with one another, all of their offspring will be tall, and variation will disappear. d. If tall and short individuals breed with one another, all offspring will be intermediate in height, and variation will disappear. ANS: D DIF: Medium REF: The Evolution of Complex Adaptations OBJ: Explain how competition, variation, and heritability lead to evolution by natural selection. MSC: Applying 46. Based on blending inheritance, which Darwin and his contemporaries believed in, if a finch with a large beak depth mates with a finch with a small beak depth, then the offspring will have a. beaks with small depth. c. beaks with large depth. b. beaks with medium depth. d. beaks with random depth. ANS: B DIF: Medium REF: Darwin’s Difficulties Explaining Variation OBJ: Explain how competition, variation, and heritability lead to evolution by natural selection. MSC: Applying 47. Why was natural selection difficult for Darwin to fully explain? a. Natural selection reduces variation. b. Natural selection acts by removing only variants of highest fitness. c. Natural selection acts by removing only variants of the lowest fitness. d. Natural selection does not actually remove any variants in real life. ANS: A DIF: Medium REF: Darwin’s Difficulties Explaining Variation OBJ: Explain how competition, variation, and heritability lead to evolution by natural selection. MSC: Remembering 48. Due to the difficulties that Darwin faced, his contemporaries continued to believe all of the following EXCEPT a. new species arise by discontinuous variation. b. new species arise by small steps. c. new species arise in a single step. d. new species can form rapidly. ANS: B DIF: Medium REF: Darwin’s Difficulties Explaining Variation OBJ: Describe why our modern understanding of the diversity of life is based on the ideas of Charles Darwin. MSC: Remembering 49. Why did Darwin’s contemporaries believe that natural selection could not move a population beyond its initial range of variation? a. Because selection cannot permanently change a population b. Because selection does not produce new variants c. Because selection can only act to stabilize variants d. Because small increments of change are highly advantageous and cannot be bred out through blending ANS: B DIF: Medium REF: Darwin’s Difficulties Explaining Variation OBJ: Describe why our modern understanding of the diversity of life is based on the ideas of Charles Darwin. MSC: Remembering ESSAY 1. Charles Darwin did not always agree with his contemporaries. What were some of his revolutionary ideas? Describe how these ideas were different from the mainstream beliefs of the nineteenth century. Lastly, discuss why we are still talking about these ideas today. ANS: To answer this question, students must be able to discuss how Darwin helped develop the following ideas: a. Before Darwin, there was no mechanistic explanation for how organisms adapt to their environmental circumstances. b. Before Darwin, most people believed that adaptations were the result of divine creation. c. Before Darwin, naturalists upheld that populations changed rapidly rather than gradually. DIF: Medium REF: Explaining Adaptation Before Darwin | Darwin’s Theory of Adaptation OBJ: Describe why our modern understanding of the diversity of life is based on the ideas of Charles Darwin. MSC: Understanding | Evaluating 2. What three conditions did Darwin conclude are necessary for natural selection to take place? Support your answer by either providing a real example from the chapter or coming up with a reasonable hypothetical example of how evolution operates. Be sure to discuss the role of the environment in your answer. ANS: To answer this question, students must be able to reiterate and understand the three postulates presented in the chapter: a. The ability of a population to expand is infinite, but the ability of any environment to support that population is finite. This results in competition for resources. b. Organisms within populations vary, and this variation affects the ability of an individual to survive and reproduce. This is because some variants will be more successful when competing for limited resources. Such variants will have greater reproductive success, and more of their offspring will have the opportunity to survive to reproductive age. c. This variation is transmitted from parents to offspring. The resulting offspring share the traits that make them more competitive in the current environment. The example that is most thoroughly explained in the chapter is the effect of drought on the finches (Geospiza fortis) of the island of Daphne Major in the Galápagos. In this example, drought resulted in larger, harder-to-open seeds and favored larger, deeper beaks. It is important to note that a change in the environment determined the direction of selection. Those individuals with larger beaks were able to survive to reproductive age. Overall, their survival and reproduction resulted in an increased mean beak depth within the population. DIF: Easy REF: Darwin’s Theory of Adaptation OBJ: Explain how competition, variation, and heritability lead to evolution by natural selection. MSC: Applying 3. Under what circumstances is selection NOT directional? Illustrate your answer with at least one example. Use your answer to explain why scientists must understand stabilizing selection in order to accurately describe evolutionary processes. ANS: Dramatic changes in the environment (like drought) create the selective pressures that favor certain traits. However, it is important to keep in mind that environmental change is random and can quickly shift back and forth. The chapter discusses how drought in the Galápagos selected for deep-beaked finches. Because drought events are sporadic, the cost of having a deep beak could quickly outweigh its benefits. To develop a deep beak, a juvenile must acquire more food resources. Because of this cost, selection can act both for and against this trait, resulting in an equilibrium state for deep beaks. They will remain in this state until an environmental pressure (like drought) acts heavily in favor of deep beaks again. Recognizing this sort of stabilizing selection is important to scientists because it explains why some complex traits take a long time to evolve whereas others arise quickly. DIF: Medium REF: Darwin’s Theory of Adaptation OBJ: Understand why natural selection can produce change or cause species to remain the same over time. MSC: Applying 4. Do adaptations always benefit the group, population, or species? Why or why not? Use real or hypothetical examples to illustrate your answer. ANS: To answer this question, students need to understand the level at which natural selection operates. Because natural selection acts on the individual, it is the individual’s reproductive success that is affected in a positive manner. What is beneficial to an individual is not necessarily beneficial to the group, population, or species. This is especially true because each individual is competing against other members of the group, population, or species for access to resources. As such, some individuals in a group may experience reduced reproductive success. The main example presented in the chapter is high-fecundity females. These females experience increased reproductive success but inflate the size of their population to the point that it exceeds the carrying capacity. DIF: Medium REF: Darwin’s Theory of Adaptation OBJ: See why natural selection usually works at the level of the individual but not at the level of the group or species. MSC: Applying 5. How does natural selection produce complex, functionally integrated adaptations like the human eye? ANS: Natural selection produces complex, functionally integrated adaptations like the human eye through the accumulation of small changes. These changes need only be slight improvements over the previous variants. If selection is cumulative, then it takes only a limited number of steps for a complex adaptation to arise. The chapter discusses the limited number of steps that it takes for a simple, light-sensitive photo receptor to evolve into a functional eye. First, the depression where the photo receptor is located becomes deeper. This step allows for the perception of directionality. As the depression becomes deeper, directional perception is enhanced. Eventually, the organism can perceive images. The last step in the process is the addition of complex neural elaborations, a cover, and eventually, a lens. DIF: Hard REF: The Evolution of Complex Adaptations OBJ: Explain how natural selection can produce very complex adaptations like the human eye. MSC: Understanding 6. What is convergent evolution? Using examples from your text, explain why convergent evolution provides evidence that complex adaptations do not occur by random chance alone. ANS: Students should recognize that convergent evolution occurs when unrelated or distantly related taxa exhibit similar adaptations. Because these organisms do not share a recent common ancestor, convergent adaptations are not a result of shared history. Instead, convergent adaptations are the result of similar selective pressures (that is, environmental conditions), which make similar traits advantageous. Therefore, convergent traits are nonrandomly favored by natural selection in both circumstances. The chapter provides the following examples of convergent evolution: (1) placental and marsupial wolves and cats and (2) the development of eyes in fish, mollusks, and other aquatic organisms. DIF: Medium REF: The Evolution of Complex Adaptations OBJ: Explain how natural selection can produce very complex adaptations like the human eye. MSC: Applying 7. When does selection produce evolutionary change relatively quickly? Provide at least two pieces of evidence to support your answer. ANS: Selection can produce evolutionary change relatively quickly if (1) a strong directional selection pressure acts constantly on a population, (2) artificial selection pressures act constantly on a population, or (3) generation times are short. The chapter provides several examples of rapid evolutionary change, including the following: • Beak size in Galápagos finches: Medium finches could reach the body size of large finches in 30–46 years if a directional selection pressure continued to act on the population over that entire time period. • Red deer on Jersey Island: Because of rising sea levels, red deer were isolated on Jersey Island for 6,000 years. During this time, they underwent a reduction in body size. • Domestication of dogs: Dogs have been artificially selected for 15,000 years or more. However, some domestic dog breeds developed over the course of hundreds of years. • Fish within the genus Poeciliopsis: Three lineages within this genus independently evolved a system of “placentation” over the course of 2.4 million years. • A simulation of the evolution of the eye: This simulation only required approximately 1,800 steps. It shows that in species with short generation times, complex traits can arise over brief periods of time. • The theoretical example of illiterate monkeys typing “Methinks it is like a weasel”: the cumulative changes that occurred and were favored took only 43 trials. If we consider that each trial represents a generation, even long generation times can lead to speedy evolutionary change. DIF: Medium REF: Rates of Evolutionary Change OBJ: Explain how natural selection can produce very complex adaptations like the human eye. MSC: Applying 8. How has an understanding of artificial selection aided our current comprehension of natural selection? ANS: Darwin drew from principles of artificial selection to explain natural selection. Artificial selection occurs when humans decide what characteristics of a domesticated animal or plant are desirable (for example, black spots on a white dog in Dalmatians, long ears in basset hounds, large kernels on corn, or large bodies in cows). Humans select for these desired characteristics by frequently mating the individuals that have them. As a result, the number of offspring with desirable characteristics increases. Artificial selection is useful in explaining natural selection because the principles are similar. With natural selection, the environment determines which characteristics are preferred, individuals with those preferred characteristics mate and produce more offspring, and preferred characteristics become more widely represented. DIF: Medium REF: Rates of Evolutionary Change OBJ: Explain how natural selection can produce very complex adaptations like the human eye. MSC: Understanding 9. What major difficulty did Darwin have with his theory of natural selection? ANS: Darwin had difficulty reconciling his theory of natural selection with the postulate that organisms within a population vary, and this variation affects the ability of individuals to survive and reproduce: • Darwin could not explain how variation is maintained. He adopted the idea of blending inheritance because Gregor Mendel had not yet completed his work on genetic recombination. • The results of blending inheritance contradict the postulate that organisms within a population vary. Ultimately, when characteristics are blended, all offspring take on a blended form, and variation is reduced. The results of natural selection also contradict the postulate that organisms within a population vary. When natural selection reduces the prevalence of unfavorable traits, variation is either greatly reduced or eliminated. If variation does not exist, then there can be no further selection. This last sentence is a crucial concept. • Darwin could not explain how new variation arose. DIF: Easy REF: Darwin’s Difficulties Explaining Variation OBJ: Describe why our modern understanding of the diversity of life is based on the ideas of Charles Darwin. MSC: Remembering CHAPTER 2: Genetics MULTIPLE CHOICE 1. Chromosomes are a. composed of ribonucleic acid. c. replicated during cell division. b. attached to organelles. d. made of proteins. ANS: C DIF: Easy REF: Cell Division and the Role of Chromosomes in Inheritance OBJ: Explain how Mendel’s laws follow from the machinery of cell replication. MSC: Remembering 2. A cross between true-breeding plants bearing yellow seeds produces offspring bearing a. all yellow seeds. c. 3 yellow seeds and 1 green seed. b. 1/2 yellow and 1/2 green seeds. d. all green seeds. ANS: A DIF: Easy REF: Cell Division and the Role of Chromosomes in Inheritance OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Understanding 3. Cross-breeding the offspring of true-bred green and yellow peas led to ________ in the second generation. a. only green individuals surviving the first days of life b. a 3:1 ratio of yellow to green offspring c. yellowish green individuals d. half the offspring being green and the other half yellow ANS: B DIF: Medium REF: Cell Division and the Role of Chromosomes in Inheritance OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Applying 4. Gametes a. are not involved in the transmission of genes. b. are the sex cells, or eggs and sperm. c. do not differ between male and female animals. d. were discovered by Darwin. ANS: B DIF: Easy REF: Mendelian Genetics OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Remembering 5. Mendel’s first principle (of segregation) states that a. characteristics from the parents blend together to produce intermediate offspring. b. characteristics from the parents do not blend together in offspring. c. only paternally derived characteristics segregate into gametes during meiosis. d. only maternally derived characteristics segregate into gametes during meiosis. ANS: B DIF: Medium REF: Chromosomes and Mendel’s Experimental Results OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Understanding 6. Mendel’s second principle (of independent assortment) states that a. eggs and sperm are formed independently of one another. b. transmission includes both blending and particulate inheritance. c. particles inherited from the mother and the father are equally likely to be transmitted to offspring. d. particles inherited from the mother are more likely to be transmitted to female offspring and particles inherited from the father are more likely to be transmitted to male offspring. ANS: C DIF: Hard REF: Chromosomes and Mendel’s Experimental Results OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Remembering 7. Chromosomes are contained in a. the gametes of prokaryotes. c. the ribosomes. b. the nuclei of eukaryotes. d. the mitochondria. ANS: B DIF: Medium REF: Mitosis and Meiosis OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Understanding 8. Homologous chromosomes a. come in pairs. b. move together into the gametes during meiosis. c. are found only in mammals. d. have three codons. ANS: A DIF: Easy REF: Mitosis and Meiosis OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Remembering 9. Mitosis a. results in half the number of chromosomes in the daughter cells. b. results in either sperm or egg. c. results in a daughter cell that has the exact copy of the chromosomes of its parent. d. results in an egg only. ANS: C DIF: Easy REF: Mitosis and Meiosis OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Remembering 10. Reduction of chromosome number occurs during a. recombination. c. somatic cell formation. b. meiosis. d. linked genes. ANS: B DIF: Medium REF: Mitosis and Meiosis OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Understanding 11. A pea plant with only green seeds is a. homozygous recessive. c. an example of blending inheritance. b. always tall. d. heterozygous. ANS: A DIF: Medium REF: Chromosomes and Mendel’s Experimental Results OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Understanding 12. If you have two parents with the genotype Aa, what is the chance that they will have an offspring with the genotype AA? a. 1/8 c. 1/4 b. 1/2 d. 1/16 ANS: C DIF: Medium REF: Chromosomes and Mendel’s Experimental Results OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Applying 13. The possible genotype(s) of a pea plant with yellow seeds is a. AA. c. Aa. b. aa. d. both a and c. ANS: D DIF: Medium REF: Chromosomes and Mendel’s Experimental Results OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Understanding 14. In diploid organisms a. chromosomes occur in homologous pairs. b. chromosomes occur in homologous triplets. c. meiosis produces diploid gametes. d. mitosis produces haploid cells. ANS: A DIF: Medium REF: Mitosis and Meiosis OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Understanding 15. In mitosis a. a haploid cell divides into two diploid cells. b. a diploid cell divides into two haploid cells. c. a haploid cell divides into two diploid cells. d. a diploid cell divides into two diploid cells. ANS: D DIF: Medium REF: Mitosis and Meiosis OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Understanding 16. Which of the following is true of mitosis? a. Mitosis produces identical daughter cells. b. Mitosis produces nonidentical daughter cells. c. Mitosis produces cells with different chromosomes. d. Mitosis produces haploid gametes. ANS: A DIF: Easy REF: Mitosis and Meiosis OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Remembering 17. In meiosis, a. haploid cells are produced from a single diploid cell. b. haploid cells are produced from two diploid cells. c. diploid cells are produced from a single diploid cell. d. diploid cells are produced from two haploid cells. ANS: A DIF: Easy REF: Mitosis and Meiosis OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Remembering 18. Which of the following is true of meiosis? a. Daughter cells contain one chromosome from each homologous pair. b. Daughter cells contain both chromosomes from each homologous pair. c. Meiosis produces somatic cells. d. Meiosis produced diploid cells. ANS: A DIF: Easy REF: Mitosis and Meiosis OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Remembering 19. Gametes a. contain both homologous chromosomes. b. are responsible for normal body growth of organisms. c. can be eggs or sperm. d. are diploid. ANS: C DIF: Easy REF: Mitosis and Meiosis OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Remembering 20. The genotype of an individual refers to a. the alleles it carries. b. its visible characteristics. c. the number of chromosomes in its sex cells. d. the number of chromosomes in its body cells. ANS: A DIF: Easy REF: Chromosomes and Mendel’s Experimental Results OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Remembering 21. The phenotype of an individual refers to a. its visible characteristics. b. the number of homologous pairs of chromosomes. c. the number of chromosomes in its body cells. d. the number of chromosomes in its sex cells. ANS: A DIF: Easy REF: Chromosomes and Mendel’s Experimental Results OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Remembering 22. An individual with two identical alleles at a locus is a. an independent phenotype. c. a heterozygote. b. a homozygote. d. dominant. ANS: B DIF: Easy REF: Chromosomes and Mendel’s Experimental Results OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Remembering 23. A heterozygote is an individual with a. the same paternal and maternal allele at a particular locus. b. a different paternal and maternal allele at a particular locus. c. a recessive allele. d. a dominant allele. ANS: B DIF: Easy REF: Chromosomes and Mendel’s Experimental Results OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Remembering 24. What genotype do true-breeding plants bearing yellow seeds have? a. aa c. Aa b. aA d. AA ANS: D DIF: Easy REF: Chromosomes and Mendel’s Experimental Results OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Understanding 25. When Mendel crossed true-breeding plants bearing yellow seeds with true-breeding plants bearing green seeds, what was the phenotypic ratio among the offspring? a. All aa individuals b. All AA individuals c. Half yellow and half green individuals d. All yellow individuals ANS: D DIF: Medium REF: Chromosomes and Mendel’s Experimental Results OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Understanding 26. What genotype do true-breeding plants bearing green seeds have? a. aa c. Aa b. aA d. AA ANS: A DIF: Easy REF: Chromosomes and Mendel’s Experimental Results OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Understanding 27. When a true-breeding plant bearing yellow seeds produces gametes, what alleles are represented among those gametes? a. Only A alleles b. Only a alleles c. Both a and A alleles, in equal frequencies d. Both a and A alleles, but mostly A alleles ANS: A DIF: Easy REF: Chromosomes and Mendel’s Experimental Results OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Understanding 28. When Mendel crossed true-breeding plants bearing yellow seeds with true-breeding plants bearing green seeds, what was the genotypic ratio among the offspring? a. 100% aa individuals c. 100% Aa individuals b. 100% AA individuals d. 3 to 1 yellow to green individuals ANS: C DIF: Medium REF: Chromosomes and Mendel’s Experimental Results OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Applying 29. Mendel crossed true-breeding plants bearing yellow seeds with true-breeding plants bearing green seeds. He then crossed the offspring from that mating with each other (F1 generation). What was the genotypic ratio among the offspring of the F1 generation? a. All Aa or aA b. 25% aa, 50% Aa/aA, and 25% AA c. All AA or aa d. 33.3% aa, 33.3% Aa/aA, and 33.3% AA ANS: B DIF: Medium REF: Chromosomes and Mendel’s Experimental Results OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Applying 30. Mendel crossed true-breeding plants bearing yellow seeds with true-breeding plants bearing green seeds. He then crossed the offspring from that mating with each other (F1 generation). What was the phenotypic ratio among the offspring? a. All yellow c. 3/4 yellow and 1/4 green b. 1/2 green and 1/2 yellow d. 3/4 green and 1/4 yellow ANS: C DIF: Medium REF: Chromosomes and Mendel’s Experimental Results OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Applying 31. When Mendel crossed heterozygote pea plants for two different traits, he recorded a phenotypic ratio of a. 1:2:1. c. 9:3:3:1. b. 4:8:4. d. 12:4. ANS: C DIF: Medium REF: Chromosomes and Mendel’s Experimental Results OBJ: Understand why genes affecting different traits are sometimes linked. MSC: Understanding 32. Recombination and crossing over are very important in the genetic process because they produce a. variation. c. DNA. b. a new somatic cell. d. linked chromosomes. ANS: A DIF: Easy REF: Linkage and Recombination OBJ: Understand why genes affecting different traits are sometimes linked. MSC: Understanding 33. What is the probability that an Aa individual will produce a gamete with an A allele? a. 100% c. 50% b. 75% d. 25% ANS: C DIF: Easy REF: Chromosomes and Mendel’s Experimental Results OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Understanding 34. Consider a cross between tall and short plants in which all of the offspring are tall. This suggests that a. the allele for tall is recessive. b. the allele for tall is dominant. c. the alleles for tall and short are codominant. d. None of the above. ANS: B DIF: Medium REF: Chromosomes and Mendel’s Experimental Results OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Understanding 35. Mendel crossed AABB with aabb individuals, where B = smooth, b = wrinkled, A = yellow, and a = green. What was the genotypic ratio of the F1 generation? a. All AAbb c. All AaBb b. 1/2 AAbb and 1/2 aaBB d. All AABB ANS: C DIF: Medium REF: Linkage and Recombination OBJ: Understand why genes affecting different traits are sometimes linked. MSC: Understanding 36. Imagine a cross between AA and Aa individuals. What is the genotypic ratio among the offspring? a. 1/2 AA and 1/2 aa c. 1/2 AA and 1/2 Aa b. 1/2 Aa and 1/2 aa d. All AA ANS: C DIF: Easy REF: Chromosomes and Mendel’s Experimental Results OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Understanding 37. Under which circumstance does Mendel’s principle of independent segregation hold? a. Only when traits are tightly linked (close together) on the same chromosome b. Only when traits are on different chromosomes c. Only when there is crossing over d. Only when the traits are not influenced by selection ANS: B DIF: Medium REF: Linkage and Recombination OBJ: Understand why genes affecting different traits are sometimes linked. MSC: Understanding 38. The law of independent segregation states that a. the fact that a gamete has an A rather than an a allele does not influence the probability that it will have a B rather than a b allele. b. alleles on different chromosomes do not influence each other as they assort into gametes. c. dominant alleles act independently of recessive alleles. d. both a and b are correct. ANS: D DIF: Medium REF: Linkage and Recombination OBJ: Understand why genes affecting different traits are sometimes linked. MSC: Understanding 39. Which of the following is true of chromosomes? a. Hereditary material is contained in the chromosomes. b. Chromosomes come in tetrads. c. Two chromosomes from each homologous pair are passed on to daughter cells during meiosis. d. One chromosome from each homologous pair is passed on to daughter cells during mitosis. ANS: A DIF: Easy REF: Chromosomes and Mendel’s Experimental Results OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Remembering 40. Imagine two loci on one chromosome. At one locus the genotype is Aa, and at the other locus the genotype is Bb. After meiosis, what are all of the possible genotypes of the gametes? a. AB and ab gametes c. AB, ab, Ab, and aB gametes b. All AB gametes d. Ab and aB gametes ANS: C DIF: Hard REF: Linkage and Recombination OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Analyzing 41. Crossing over a. can occur between loci on nonhomologous chromosomes. b. can occur between alleles on the same chromosome. c. increases genetic variation. d. decreases genetic variation. ANS: C DIF: Medium REF: Linkage and Recombination OBJ: Understand why genes affecting different traits are sometimes linked. MSC: Understanding 42. When two loci are very close together on a chromosome, a. they are linked. b. a crossing-over event between them is less likely than when two loci are far apart. c. they can blend into a single gene. d. both a and b are correct. ANS: D DIF: Medium REF: Linkage and Recombination OBJ: Understand why genes affecting different traits are sometimes linked. MSC: Applying 43. Molecular genetics a. links biology to geophysics. b. has explained the way the solar system works. c. has demonstrated that humans descended from chimpanzees. d. provides data for reconstructing the evolutionary history of species. ANS: D DIF: Easy REF: Molecular Genetics OBJ: Explain how the properties of DNA are consistent with the role of genes in inheritance. MSC: Remembering 44. Analysis of DNA sequences tells us that a. humans and chimpanzees share a more recent common ancestor than either shares with gorillas. b. the last common ancestor of chimpanzees and humans were gorillas. c. humans left Asia about 1 million years ago. d. humans left Asia and went to Africa. ANS: A DIF: Medium REF: Molecular Genetics OBJ: Explain how the properties of DNA are consistent with the role of genes in inheritance. MSC: Understanding 45. The structure of DNA is that a. of a series of intertwining chromosomes. b. of a double-stranded molecule, consisting of four bases. c. of a series of bases: adenine, guanine, thymine, and cytosine. d. both b and c are correct. ANS: D DIF: Medium REF: Molecular Genetics OBJ: Explain how the properties of DNA are consistent with the role of genes in inheritance. MSC: Understanding 46. Which of the following statements is true? a. DNA has a nonrepeating four-base structure. b. DNA is contained in chromosomes. c. DNA stands for determining nuclear acid. d. DNA does not tell us why heredity leads to the patterns Mendel described in pea plants. ANS: B DIF: Easy REF: Genes Are DNA OBJ: Explain how the properties of DNA are consistent with the role of genes in inheritance. MSC: Remembering 47. Exact replication of DNA is possible because a. the low number of possible nucleotides. b. base-pair complementarity. c. the sequence of nucleotides along the DNA, which is always the same. d. both a and c are correct. ANS: B DIF: Easy REF: Genes Are DNA OBJ: Explain how the properties of DNA are consistent with the role of genes in inheritance. MSC: Understanding 48. Sickle-cell anemia a. is on the decline. b. is caused by the change in two amino acids that make up the hemoglobin molecule. c. results when hemoglobin molecules do not fold correctly, reducing their ability to bind to oxygen. d. increases an individual’s susceptibility to malaria. ANS: C DIF: Medium REF: Some Genes Code for Proteins OBJ: Describe how genes control the structure of proteins and influence the properties of organisms. MSC: Applying 49. Unlike a eukaryote, a prokaryote a. does not have DNA. c. has a large number of chromosomes. b. has many introns and exons. d. does not have a nucleus. ANS: D DIF: Medium REF: Some Genes Code for Proteins OBJ: Describe how genes control the structure of proteins and influence the properties of organisms. MSC: Remembering 50. Alternative splicing a. allows the same DNA sequence to code for more than one protein. b. allows prokaryote exons to be included in the genome of eukaryotes. c. allows only certain sections of DNA to be copied. d. allows a maximum of four exons to be attached to mRNA. ANS: A DIF: Hard REF: Some Genes Code for Proteins OBJ: Describe how genes control the structure of proteins and influence the properties of organisms. MSC: Applying 51. Some biologists hypothesize that introns are maintained in eukaryotes because their population sizes are much smaller than in prokaryotes. ________ is the random, nonadaptive evolutionary process that explains this phenomenon. a. Genetic drift c. Protein synthesis b. Natural selection d. Transcription ANS: A DIF: Hard REF: Some Genes Code for Proteins OBJ: Describe how genes control the structure of proteins and influence the properties of organisms. MSC: Analyzing 52. If the DNA codon for an amino acid is ACC, what are the mRNA and its tRNA anticodon, respectively? a. TGG; UCC c. GTG; CAC b. GGT; CCA d. UGG; ACC ANS: D DIF: Medium REF: Genes Are DNA OBJ: Explain how the properties of DNA are consistent with the role of genes in inheritance. MSC: Applying 53. Which of the following is true of DNA transcription/translation? a. A codon corresponds to an amino acid. b. A DNA sequence codes for a protein. c. A protein consists of a series of codons. d. Both a and b are true. ANS: D DIF: Medium REF: Some Genes Code for Proteins OBJ: Describe how genes control the structure of proteins and influence the properties of organisms. MSC: Understanding 54. Because there are 64 possible codons and only 20 amino acids, a. many mutations have no effect on phenotype. b. every mutation has some effect on phenotype. c. each tRNA molecule contains two extra amino acids. d. each tRNA molecule contains two extra codons. ANS: A DIF: Medium REF: Some Genes Code for Proteins OBJ: Describe how genes control the structure of proteins and influence the properties of organisms. MSC: Understanding 55. Which of the following sequences is accurate for transcription and translation? a. DNA tRNA mRNA protein c. Protein tRNA DNA b. DNA mRNA protein d. Protein tRNA DNA ANS: B DIF: Medium REF: Some Genes Code for Proteins OBJ: Describe how genes control the structure of proteins and influence the properties of organisms. MSC: Understanding 56. As DNA codes for proteins, it can be interrupted by noncoding sequences called a. organelles. c. introns. b. proteins. d. synthetases. ANS: C DIF: Easy REF: Some Genes Code for Proteins OBJ: Describe how genes control the structure of proteins and influence the properties of organisms. MSC: Remembering 57. The presence of repressors and activators in regulatory genes means that there is ________ of gene expression. a. translation c. a biochemical pathway b. combinatorial control d. primary structure ANS: B DIF: Hard REF: Regulatory Sequences Control Gene Expression OBJ: Explain how gene regulation allows the same genes to control the development and function of many different parts of the body. MSC: Understanding 58. The organelles that splice the mRNA in eukaryotes after the introns have been snipped out are called a. splitosomes. c. spliceosomes. b. ribosomes. d. Golgi bodies. ANS: C DIF: Medium REF: Not All DNA Codes for Protein OBJ: Explain how gene regulation allows the same genes to control the development and function of many different parts of the body. MSC: Remembering 59. ________ binds to complementary mRNA molecules and regulates the translation of mRNA into proteins. a. Transfer RNA c. Noncoding DNA b. MicroRNA d. Mitochondrial RNA ANS: B DIF: Medium REF: Not All DNA Codes for Protein OBJ: Explain how gene regulation allows the same genes to control the development and function of many different parts of the body. MSC: Understanding 60. At least ________ of the genome is expressed as noncoding DNA. a. 50% c. 75% b. 25% d. 5% ANS: A DIF: Easy REF: Not All DNA Codes for Protein OBJ: Explain how gene regulation allows the same genes to control the development and function of many different parts of the body. MSC: Remembering ESSAY 1. How do the results of Mendel’s experiments affect our understanding of how variation is preserved? ANS: To answer this question fully, students should discuss genotypes and phenotypes; dominant and recessive genes; and heterozygotes, particulate inheritance, and the facts that one gene is inherited from each parent and that each gene/allele is equally likely to be transmitted to gametes and therefore transmitted to the next generation. For any given phenotype, or physical characteristic, there is at least one genotype (combination of genes or alleles) that codes for that phenotype. Therefore, there can be several variants of genes, which are called alleles. For example, Mendel’s pea plants had two alleles for seed color, one for yellow (abbreviated Y) and one for green (abbreviated y). The yellow allele is dominant because plants that are both homozygous for yellow seeds (YY) and heterozygous (Yy) have yellow seeds, whereas for a plant to have green seeds it must be homozygous for green (yy), or homozygous recessive. But Mendel determined that variation is preserved through the selective breeding of the offspring (F1 generation) of yellow- and green-seeded pea plants that bred true, that is, heterozygotes. The F2 generation produced both yellow- and green-seeded individuals in a ratio of 3:1. So even though the green variants appeared to be lost in the F1 generation, this phenotype reappeared in the F2 generation. This occurrence is connected to the laws of particulate inheritance and independent assortment: random chance determines which allele will be passed on to the offspring, and each allele has an equal chance of being passed on. DIF: Medium REF: Chromosomes and Mendel’s Experimental Results OBJ: Describe how experiments by Gregor Mendel revealed the logic of inheritance. MSC: Applying 2. Imagine a cross between two AaBb individuals, where A = yellow, a = green, B = smooth, and b = wrinkled. What is the genotypic and phenotypic ratio among the offspring? ANS: This question is best answered using a Punnett square, although students may be able to remember the ratios. Having two alleles for two traits results in sixteen possible combinations, assuming independent assortment (the other of Mendel’s laws). If two heterozygotes are crossed, the next generation has a phenotype ratio of 9:3:3:1 (9 smooth-yellow; 3 smooth-green; 3 wrinkled-yellow; 1 wrinkled green). The genotype ratio is 1AABB: 2AABb: 1AAbb: 2AaBB: 4AaBb: 2Aabb: 1aaBB: 2aaBb: 1aabb. DIF: Medium REF: Chromosomes and Mendel’s Experimental Results | Linkage and Recombination OBJ: Understand why genes affecting different traits are sometimes linked. MSC: Applying 3. Compare and contrast mitosis and meiosis. Include in your discussion for each process (a) the number of daughter cells produced and (b) the number of chromosomes each new cell contains. What are recombination and crossing over, and why are they important in the study of evolution? ANS: Mitosis occurs in somatic or body cells, requires a single replication of the chromosomes, and results in two daughter cells both with the full complement of chromosomes (in eukaryotes referred to as the diploid number, abbreviated as 2N). In contrast, meiosis occurs in the sex cells or gametes and requires a single replication of chromosomes, but because the cell divides twice, it results in four daughter cells with half of the chromosomes, one copy of each. These cells are haploid, abbreviated as N. Crossing over occurs during meiosis, when the replicating chromosomes line up (tetrad), become damaged, break, and recombine. Therefore, recombination is the result of crossing over. The end result is that the gametes contain, and therefore offspring inherit, a novel combination of genes that is not present in the parent. This is important for evolution because it is a source of variation, upon which natural selection acts. DIF: Medium REF: Mitosis and Meiosis OBJ: Describe how experiments by Gregor Mendel’s laws follow from the machinery of cell replication. MSC: Understanding 4. Consider a homologous pair of chromosomes with the genotype Aa at one locus and the genotype Bb at another locus. After undergoing meiosis, what are all of the possible genotypes of the gametes produced? ANS: The likely genotypes of the gametes will depend on how close these two loci are the closer the loci, the less likely crossing over will result in recombination, and the farther away they are, the more likely