1. CHAPTER 7 “TAKE-HOME MESSAGE” 7.1 How many alleles of each gene do you have? Where did you get them?
Answer: Individuals have two copies (alleles) of each gene, having inherited one from each patent. 7.2 Give two examples of single-gene traits, genetic traits determined by alleles of a single gene. Answer: The book lists cleft vs. non-cleft chins, attached vs. unattached earlobes, and widow’s peaks vs. straight hairlines, as well as fish odor syndrome. You may be able to think of other examples. 7.3 Why was the pea plant a good organism with which to study heredity?
Answer: The pea plant works well as a subject of inheritance study because the plants produce many offspring in a relatively short amount of time and it is easy carefully control crosses through fertilization. 7.4 How did Gregor Mendel explain that some purple-flowered pea plants could produce white-flowered offspring?
Answer: Each pea plant has two copies (alleles) of the gene for flower color. The purple-flowered plants in question had one copy of the purple allele and one copy of the white allele, but appeared purple since this allele was dominant. Some of their offspring received a recessive white allele from both parents, and therefore had white flowers.
7.5 What is listed across the axes of a Punnett square? What is listed inside the boxes of a Punnett square? Answer: A Punnett square can be used to determine the possible outcomes of a cross between two individuals. The genotypes of the gametes these individuals can produce are listed across the axes, and the genotypes of their potential offspring are listed inside the boxes of the Punnett square. 7.6 What is the chance that two giraffes heterozygous for the recessive albinism allele will produce an albino offspring?
Answer: For the offspring to be albino, it would have to inherit a recessive albinism allele (a) from both parents. The probability of this event it 0.5 (the chance that the mother’s gamete contains a) times 0.5 (the chance that the father’s gamete contains a), for a probability of 0.25.
7.7 If a normally pigmented alligator crossed with a white alligator produces some normally pigmented offspring and some white offspring, what can you conclude regarding this normally pigmented alligator? Answer: Since the white coloration is a recessive trait, offspring would have to receive a recessive white allele from both parents. Therefore, the normally pigmented alligator in question must be a heterozygote, possessing one allele for normal pigmentation and one allele for white pigmentation. This type of cross is called a test cross.
2. 7.9 When a red-flowered snapdragon is crossed to a white-flowered snapdragon, all of the offspring have pink flowers. Explain this observation. Answer: Since the pink-flowered offspring display a phenotype intermediate between red and white, this is an example of incomplete dominance. These offspring inherited a red allele from one parent and a white allele from the other parent.
7.10 What alleles are possessed by a person with type A blood? How about type AB blood?
Answer: Individuals with type A blood must have an A allele, but their second allele of this gene can be either A or O, since the A allele is dominant to the O allele. Individuals with type AB blood must have one A allele and one B allele. 7.11 Give two examples of polygenic traits, traits influenced by multiple genes with additive effects.
Answer: The book lists human height, skin color, eye color, and autism. You may be able to think of other examples.
CHAPTER 8 “TAKE-HOME MESSAGE” 8.1 The starvation-resistance experiment involving fruit flies described in the text is an example of evolutionary change. Can you think of other potential examples of the characteristics of a population changing over time in a manner that we can observe and even cause?
Answer: The textbook mentions the breeding of dogs for size and the breeding of rabbits for speed. You may be able to think of other examples.
8.2 Give at least two examples of observations that helped chip away at the idea of a relatively young and unchanging earth.
Answer: The book describes Buffon’s suggestion that the earth was much older than previously believed, Cuvier’s fossil evidence that extinction had occurred, Lamarck’s suggestion that living species change over time, and Lyell’s argument that geological forces that gradually shaped the earth continue to do so. 8.3 Name one of the places where Darwin studied the natural world during his ‘round-the-world voyage. Answer: The Galápagos Islands off of Ecuador in South America are the most famous site of Darwin’s fieldwork while serving on the Beagle. He also studied in Brazil, Patagonia, and other sites in South America, as well as in Africa, Australia, and many islands in the Pacific and Indian Oceans.
8.4 Give an example, other than finches, of an observation made by Darwin during his voyage that helped him develop his theory of how species might change over time.
Answer: The textbook gives the example of the modern day armadillo and its striking similarities to the much larger, extinct glyptodont.
3. 8.5 What convinced Darwin to finally publish his theory of natural selection as the means of evolution after it sat idle for over 15 years?
Answer: Alfred Russel Wallace independently arrived at the same theory, so Darwin needed to publish his work to get credit for developing the theory. 8.6 Describe the relationship between evolution and natural selection. Can individuals evolve?
Answer: Evolution refers to a change in characteristics of a population over time, while natural selection is the mechanism of this change. Populations change; individuals do not.
8.7 Why are mutations important in evolution, when most mutations are harmful?
Answer: Mutation is the only way new alleles are created within a population. Although most are harmful, a very small number of mutations are beneficial. Through time, these beneficial mutations can become more numerous within a population as the population adapts to the environment.
8.8 Why would a characteristic such as having a cleft chin change within a population over time, if this trait doesn’t help or hurt an individual?
Answer: Cleft chins are as likely to increase in a population over time as they are to decrease. The changes are random, and not in response to the environment.
8.9 In 1400, almost all North Americans possessed brown eyes. Today, many North Americans possess blue eyes. Explain the basis for this evolutionary change.
Answer: Blue-eyed alleles entered North American populations through gene flow as some blue-eyed Europeans migrated into North America.
8.10 Why would faster rabbits tend to have more offspring than slower rabbits? What effect would this have on the next generation of rabbits?
Answer: Slower rabbits are more likely to get eaten by predators such as foxes, and faster rabbits are more likely to escape predators like foxes. A larger number of the fast rabbits will survive, and only the surviving rabbits are able to reproduce. The next generation of rabbits would tend to be slightly faster on average, since these are the traits passed on in larger numbers. 8.12 Who has greater fitness: a world-class bodybuilder with a single child, or an overweight, middle-aged accountant with four children?
Answer: Fitness is a measure of reproductive output, not physical stature. The accountant with four children would therefore have a higher fitness than the bodybuilder in this example. 8.13 Mutation, genetic drift, gene flow, and natural selection can all result in evolutionary change. Which of these make a population better adapted to its environment?
Answer: Of these four agents of evolutionary change, only natural selection results in adaptive evolution. 8.14 Is there a “perfect” beak size for a seed-eating finch in the Galápagos Islands?
4. Answer: No. During dry years in which small and easily-cracked seeds are plentiful, a larger beak would be more helpful in cracking larger seeds and would therefore be more ideal. During rainy years in which small and easily-cracked seeds were plentiful, smaller beaks would be advantageous and would therefore be more ideal. What is optimal or “perfect” in one environment may be very suboptimal or imperfect in another environment. 8.15 Dog, horse, and pigeon breeds are produced through artificial selection. How many more examples can you think of?
Answer: The book also discusses the various varieties of apples, but there are many additional examples that will be familiar to you, such as cats, various types of flowers, various crop plants. 8.16 The book gives examples of directional, stabilizing, and disruptive selection. Give at least one more example of natural selection, and the type of change that results.
Answer: There are many possible answers for this question—for instance—predator- prey and parasite-host. These are examples of directional selection. 8.17 How could an insect wing evolve, when half a wing does not allow flight or gliding?
Answer: Structures often first appear because they serve some other purpose. For example, a small nub or “almost-wing” that does not allow flight might improve temperature regulation. 8.18 Tiktaalik is a “missing link” between fish and land animals. What features of this creature are fish-like? What features are land animal-like?
Answer: Tiktaalik has gills, scales, and fins like a fish, but also possessed arm-like joints and could drag itself across the land.
8.22 The book describes changes of grass in different areas on a golf course as an observable example of evolution. Can you think of another?
Answer: The book also describes the occurrence of antibiotic-resistant bacteria as another observable example of evolution. You may be able to think of others. Convergent evolution Vestigial structures
CHAPTER 9 “TAKE-HOME MESSAGE”
9.1 List two examples of behaviors that are influenced by natural selection. Answer: The book lists fatty food and taste preference, feeding behavior, maternal care, and singing behavior in songbirds. There are many other examples because natural selection can shape behaviors just as it shapes changes in physical traits.
9.2 Define fixed action pattern and provide an example.
5. Answer: A fixed-action pattern is a sequence of behavior triggered under certain conditions that requires no learning, does not vary, and once started, runs to completion. The book lists egg-retrieval in geese and aggressive displays and attacks by stickleback fish as examples. You may be able to think of others. Instincts. 9.3 Why do monkeys learn to fear snakes more readily than they learn to fear flowers?
Answer: Some behaviors must be learned by observation, but behaviors that are most important to survival are more easily learned than behaviors that do not affect survival. Fear of snakes is a behavior that is learned easily by all (or nearly all) individual monkeys. This is called prepared learning.
9.4 Do animals try to maximize their reproductive success? Explain.
Answer: Natural selection doesn’t have to produce animals consciously trying to maximize reproductive success; it only needs to produce animals that behave in a way that actually results in reproductive success. Behaviors that lead to an outcome that increases the animal’s relative reproductive success will be favored by natural selection, even if the animal is not aware of it. 9.6 How can you explain why older female Belding’s ground squirrels are more likely to make alarm calls than younger females, who in turn are more likely to make alarm calls than males?
Answer: Alarm calling is all about protecting relatives; the more kin an individual is likely to have, the more likely it is to sound the alarm. Older females are likely to have the largest number of relatives, while adult males having traveled to a new colony shortly after reaching maturity are likely to have the least number of relatives in the colony. Kin selection
9.7 How would it benefit a vampire bat to regurgitate blood to assist an unrelated individual? Answer: Blood sharing in vampire bats is an example of reciprocal altruism. The bat giving blood to a starving bat may some day receive blood from an unrelated bat when it is itself starving.
9.8 Give an example of a behavior that is maladaptive when organisms are in environments different from the environment to which they are adapted.
Answer: The book describes donations to refugees in another continent and alarm calling in female Belding’s ground squirrels transplanted to an unrelated colony. You may be able to think of other examples. Vervet monkeys
9.9 Does evolution seem to favor individuals that behave in a manner that benefits a group, but reduces the individual’s inclusive fitness?
Answer: No. Individuals generally act in ways that increase their reproductive success because those who value their own reproductive success above that of others are more likely to produce many offspring and pass the “selfish” genes on to the next generation. 9.10 In what ways is a female mammal’s reproductive investment commonly greater than a male’s investment?
6. Answer: Eggs require greater energy investments than sperm. The growth and development of offspring within the female’s body requires a significant energy investment by the female. Lactation also requires a significant energy investment by the female. 9.11 In one sentence each, describe the two differences that have evolved in the sexual behavior of males and females.
Answer: The sex with the greater energetic investment in reproduction, almost always the females, will be more discriminating when it comes to mating. Members of the sex with less energetic investment in reproduction, almost always the males, will compete among themselves for access to the other sex. 9.14 How does parental investment correlate with mating patterns?
Answer: When males and females have similar parental investments, monogamy is common. When the parental investment of the female is much higher than that of the male, polygyny is common. 9.15 How does sexual dimorphism correlate with mating patterns?
Answer: A significant increase in size between males and females is common in polygynous species where males fight among themselves for access to multiple females.
9.16 What are the three most common types of communication signals used by animals? Answer: Animals most commonly use chemical means such as pheromones, acoustical means such as alarm calls, and visual cues such as the honeybee waggle dance. 9.17 What is meant by an honest signal?
Answer: An honest signal is a signal that cannot be faked and that is given when both the individual making the signal and the individual responding to it have the same information about an individual or situation.
Black widow mating
Bush crickets
Polygyny
CHAPTER 10 “TAKE-HOME MESSAGE” 10.1 What types of organic molecules were formed in the Urey-Miller experiment, in which their best estimate of the environment of the early earth was recreated?
Answer: Within a matter of days, they discovered numerous organic molecules, including five of the twenty amino acids. Later analysis with more sensitive equipment revealed that all twenty of the amino acids were formed.
7. Which of the following molecules was NOT present in the prebiotic environment?
Question options:
hydrogen sulfide (H2S)
ammonia (NH3)
methane (CH4)
molecular oxygen (O2)
water (H20) Age of the Earth?
Fossils
Oldest fossils?
10.2 Give a general explanation as to why it is harder to define life among collections of molecules (such as those that were the earliest forms of life on earth) than among humans.
Answer: Because whether a human is living or non-living is obvious, while among the molecules it is anything but obvious. There is no generally accepted precise definition of life, but most scientists agree on two essential characteristics: the ability to replicate and the ability to carry out some sort of metabolism. Clearly determining these conditions— especially the ability to carry out metabolism—is complicated and subject to rigorous and continuing scientific debate and discovery. 10.3 There are two general types of barriers that result in the reproductive isolation of species: Prezygotic barriers that prevent mating or prevent fertilization, and postzygotic barriers that function after fertilization and prevent the formation of healthy or fertile offspring. What do these two types of barriers have in common?
Answer: Both of these two general types of barriers prevent the permanent flow of genes between two populations representing separate species.
10.4 Are all animals eukaryotes? Are all eukaryotes animals? Explain. Answer: All animals are eukaryotes, but not all eukaryotes are animals. Domain Eukarya is presently divided into four kingdoms, the protists, plants, fungi and animals. Given this division, all animals do belong to the eukaryotic domain, but there are members of the eukaryotic domain that are classified into kingdoms other than the animal kingdom. 10.5 Although the biological species concept is very powerful and useful, it falls short under the five situations. Describe two of the circumstances under which it is difficult to classify species using the biological species concept?
8. Answer: 1) Asexually reproducing species cannot be classified on the basis of a nonexistent sexual cycle. 2) Species represented in the fossil record are no longer able to reproduce, so they must be classified on a different basis. 3) The process of speciation rarely displays a definitive moment separating the parental species and the newly formed species. 4) Species may have individuals at different parts of their range than cannot reproduce, but that are connected through populations in more central regions of the range. 5) Some closely related species are capable of hybridizing to produce healthy and fertile offspring.
10.6 There are the two phases required for speciation to occur. The first phase of speciation is reproductive isolation, in which two populations stop sharing their genetic material with each other. This phase is followed by genetic divergence, in which the genetic differences between these two populations increase over time. What causes genetic divergence to occur?
Answer: Genetic divergence is largely due to adaptations in response to different environmental conditions.
10.7 If you visualize the history of life, what is represented by the tips of the branches? What is represented by the node, the point where two branches diverge?
Answer: The tips of the branches represent the millions or tens of millions of species on the earth. The nodes, where branches separate, represent points where a common ancestor diverged into two separate species.
10.8 Describe why animals and fungi together represent a monophyletic group. Answer: Monophyletic groups represent groupings of species in which all individuals are more closely related to each other than to any individuals outside of the group. Animals and fungi together represent a monophyletic group because they share a more recent common ancestor with each other than with any outside group such as plants.
10.9 Which is a better indicator of a close evolutionary relationship, similarities in structure or similarities in DNA sequences? Explain. Answer: Similarities in structure are commonly a result of shared ancestry (homologous features), but are sometimes the result of independent evolution in response to similar environmental conditions (analogous features). Similarities in DNA sequences are more accurate in determining evolutionary relationships. 10.10 Microevolution refers to evolutionary changes within a species, while macroevolution refers to larger-scale evolutionary change that forms new species. Both are similar in that they involve adaptation to the environment, and both occur through an accumulation of allele changes over time. But what is the relationship between macroevolution and microevolution?
Answer: Macroevolution is simply the extension of microevolution over a greater span of time. 10.11 Punctuated equilibrium has been erroneously portrayed as a “problem” for evolutionary biology because it has been mistakenly believed that the rapid evolutionary changes of punctuated equilibrium are the result of some new mechanism for evolution. Why is this view incorrect?
9. Answer: Punctuated change can appear fast, but only on a geologic time scale. The per- generation rates of change necessary to produce punctuated change are not above the rates of change that have been measured in evolving populations. 10.13 What is the fundamental difference between background and mass extinctions other than differences in rates? Answer: Background extinctions are caused mostly as a result of natural selection. Mass extinctions are due to extraordinary and sudden changes to the environment such as the asteroid that brought about the extinction of the dinosaurs. 10.14 All life in currently classified into three domains, bacteria, archaea, and eukarya. Previously there were widely accepted systems that classified life into two kingdoms and five kingdoms. Do such fundamental changes indicate a problem with science?
Answer: Not at all. Changes in classifications have come about as a result of scientists continually striving to come up with better answers to questions. Each succeeding classification method has been the result of important questions being asked, new discoveries being made, and better answers being developed. 10.17 Eukaryotes are classified into four kingdoms – plants, animals, fungi, and protists. Which of these is the most diverse and likely to be split into smaller kingdoms and why is so little known about it?
Answer: Of these groups, the protists are the most diverse, and will likely be split into multiple smaller kingdoms. Like bacteria and archaea, it is most often invisible to the naked eye and we tend to know more about that which we can easily see and observe
