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Genetics: A Conceptual Approach, 5th Edition Solution Manual

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    Chapter One: Introduction to Genetics COMPREHENSION QUESTIONS Section 1.1 *1. How did Hopi culture contribute to the high incidence of albinism among members of the Hopi tribe? Solution: In Hopi culture, albino individuals were considered special and awarded special status in the village. Hopi male albinos were not required to work the fields, thus avoiding extensive exposure to sunlight that could prove damaging or deadly. Because the male albinos remained in the village during the day, they had mating advantages over the males who participated in farming and other duties outside of the village. Albinism was considered to be a positive trait reflecting the purity of the villagers. Finally, the small population size of the Hopi tribe may have helped increase the allele frequency of the albino gene due to chance. 2. Outline some of the ways in which genetics is important to all of us. Solution: Genetics directly influences our lives and is fundamental to what and who we are. For example, genes affect our appearance (e.g., eye color, height, weight, skin pigmentation, and hair color). Our susceptibility to diseases and disorders is affected by our genetic makeup. Genetics plays a significant role in researching and developing techniques to diagnose and treat these hereditary diseases. Genes may also influence our intelligence and personality. Genetic techniques have enabled scientists to develop genetically modified crops that are resistant to pesticides and herbicides or that have enhanced nutritional properties making it possible to produce larger quantities of food for the world’s growing population. Lastly, genetic engineering has made it possible to mass produce pharmaceuticals and other substances of commercial value. 3. Give at least three examples of the role of genetics in society today. Solution: Genetics plays important roles in the diagnosis and treatment of hereditary diseases: in breeding plants and animals for improved production and disease resistance; and in producing pharmaceuticals and novel crops through genetic engineering. 4. Briefly explain why genetics is crucial to modern biology.

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    2 Chapter One: Introduction to Genetics Solution: Genetics is crucial to modern biology in that it provides unifying principles: The genetic code is universal, meaning that all organisms use nucleic acid as their genetic material, and all organisms encode genetic information in the same manner. The study of many other biological disciplines, such as developmental biology, ecology, and evolutionary biology, is supported by genetics. 5. List the three traditional subdisciplines of genetics and summarize what each covers. Solution: 1) Transmission (classical) genetics is concerned with the inheritance of genes from one generation to the next. It also deals with the location of genes on chromosomes and gene- mapping. 2) Molecular genetics focuses on the structure, organization, and function of genes at the molecular level. Molecular genetics is also concerned with the processes by which genetic information is transferred and expressed. 3) Population genetics studies genetic variation and changes in genes and allele frequencies within groups of individuals of the same species over time. 6. What are some characteristics of model genetic organisms that make them useful for genetic studies? Solution: Model genetic organisms have relatively short generation times, produce numerous progeny, are amenable to laboratory manipulations, and can be maintained and propagated inexpensively. Section 1.2 7. When and where did agriculture first arise? What role did genetics play in the development of the first domesticated plants and animals? Solution: Agriculture first arose 10,000 to 12,000 years ago in the area now referred to as the Middle East (i.e., Turkey, Iran, Iraq, Syria, Jordan, and Israel). Early farmers selectively bred individual wild plants or animals that had useful characteristics with others that had similar useful traits. The farmers then selected for offspring that contained those useful features. Early farmers did not completely understand genetics, but they clearly understood that breeding individual plants or animals with desirable traits would lead to offspring that contained these same traits. This selective breeding led to the development of domesticated plants and animals. 8. Outline the notion of pangenesis and explain how it differs from the germ-plasm theory.

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    Chapter One: Introduction to Genetics 3 Solution: Pangenesis theorizes that information for creating each part of the offspring’s body originates from each respective part of the parent’s body and is passed through the reproductive organs to the embryo at conception. Pangenesis suggests that changes in parts of the parent’s body may be passed to the offspring’s body. The germ-plasm theory, in contrast, states that the reproductive cells (eggs and sperm) possess all of the information required to make the complete body; the rest of the body contributes no information to the next generation. 9. What does the concept of the inheritance of acquired characteristics propose and how is it related to the notion of pangenesis? Solution: The theory of inheritance of acquired characteristics postulates that traits acquired during one’s lifetime can be transmitted to offspring. It developed from pangenesis, which postulates that information from all parts of one’s body is transmitted to the next generation. Thus, according to the theory of inheritance of acquired characteristics, the development of large bicep muscles through exercise would produce children with large biceps. 10. What is preformationism? What did it have to say about how traits are inherited? Solution: Preformationism is the theory that the offspring results from a miniature adult that is already preformed in the sperm or the egg. All traits would thus be inherited from only one parent, either the father or the mother, depending on whether the homunculus (the preformed miniature adult) resided in the sperm or the egg. 11. Define blending inheritance and contrast it with preformationism. Solution: The theory of blending inheritance proposes that the egg and sperm from two parents contains material that blends upon conception, influencing the development of the offspring. This theory indicates that the offspring is an equal blend of the two parents. In preformationism, the offspring inherits all of its traits from one parent. 12. How did developments in botany in the seventeenth and eighteenth centuries contribute to the rise of modern genetics? Solution: Botanists of the seventeenth and eighteenth centuries discovered that plants reproduce sexually, enabling them to develop new techniques for crossing plants and creating plant hybrids. These early experiments provided essential background work for Mendel’s plant crosses. Mendel’s work laid the foundation for the study of modern genetics. 13. List some advances in genetics made in the twentieth century.

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    4 Chapter One: Introduction to Genetics Solution: 1902 Proposal that genes are located on chromosomes by Walter Sutton 1910 Discovery of the first genetic mutation in a fruit fly by Thomas Hunt Morgan 1930 The foundation of population genetics by Ronald A. Fisher, John B. S. Haldane, and Sewall Wright 1940s The use of viral and bacterial genetic systems 1953 Three-dimensional structure of DNA described by Watson and Crick 1966 Deciphering of the genetic code 1973 Recombinant DNA experiments 1977 Chemical and enzymatic methods for DNA sequencing developed by Walter Gilbert and Frederick Sanger 1986 PCR developed by Kary Mullis 1990 Gene therapy 14. Briefly explain the contribution that each of the following persons made to the study of genetics. Solution: a. Matthias Schleiden and Theodor Schwann Proposed the concept of the cell theory, which indicated that the cell is the fundamental unit of living organisms. Caused biologists interested in heredity to examine cell reproduction. b . August Weismann Proposed the germ-plasm theory, which holds that cells in reproductive organs carry a complete set of genetic information. c. Gregor Mendel First discovered the basic rules of inheritance. d. James Watson and Francis Crick Along with Rosalind Franklin and Maurice Wilkins, described the three-dimensional structure of DNA. e. Kary Mullis Developed the polymerase chain reaction, used to quickly amplify small amounts of DNA. Section 1.3 15. What are the two basic cell types (from a structural perspective) and how do they differ? Solution: The two basic cell types are prokaryotic and eukaryotic. Prokaryotic cells have neither membrane-bound organelles nor a true nucleus. Their chromosomes are found within the cytoplasm. Eukaryotic cells possess a membrane-bound nucleus and other membrane- bound organelles such as an endomembrane system and mitochondria. 16. Outline the relations between genes, DNA, and chromosomes.

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    Chapter One: Introduction to Genetics 5 Solution: A gene is a particular DNA nucleotide sequence that encodes an individual trait. Genes are located at specific positions on chromosomes. APPLICATION QUESTIONS AND PROBLEMS Section 1.1 *17. What is the relation between genetics and evolution? Solution: In essence, evolution is change in the genetic composition of a population over generations. Mutations generate new genetic variants, recombination generates new combinations of genetic variants, and natural selection or other evolutionary processes cause a change in the proportions of specific genetic variants in the population. *18. For each of the following genetic topics, indicate whether it focuses on transmission genetics, molecular genetics, or population genetics. a. Analysis of pedigrees to determine the probability of someone inheriting a trait Solution: Transmission genetics b. Study of people on a small island to determine why a genetic form of asthma is prevalent on the island Solution: Population genetics c. Effect of nonrandom mating on the distribution of genotypes among a group of animals Solution: Population genetics d. Examination of the nucleotide sequences found at the ends of chromosomes Solution: Molecular genetics e. Mechanisms that ensure a high degree of accuracy in DNA replication

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    6 Chapter One: Introduction to Genetics Solution: Molecular genetics f. Study of how the inheritance of traits encoded by genes on sex chromosomes (sex- linked traits) differs from the inheritance of traits encoded by genes on nonsex chromosomes (autosomal traits) Solution: Transmission genetics 19. Describe some of the ways in which your own genetic makeup affects you as a person. Be as specific as you can. Solution: Answers will vary but should include observations similar to those in the following example: Genes affect my physical appearance; for example, they probably have largely determined the fact that I have brown hair and brown eyes. Undoubtedly, genes have affected my height of five feet, seven inches, which is quite close to the height of my father and mother, and my slim build. My dark complexion mirrors the skin color of my mother. I have inherited susceptibilities to certain diseases and disorders that tend to run in my family; these include asthma, a slight tremor of the hand, and vertigo. 20. Describe at least one trait that appears to run in your family (appears in multiple members of the family). Does this trait run in your family because it is an inherited trait or because it is caused by environmental factors that are common to family members? How might you distinguish between these possibilities? Solution: Answers will vary but should include observations similar to those in the following example: My two brothers and I share two traits: we are all three taciturn (we don’t speak much) and smart (just don’t ask my teenage daughter). Although the literature provides evidence for a genetic component for intelligence, I’m not aware of any studies on the heritability of being taciturn. If I were to investigate to what extent these traits are determined by the environment or by heredity, I would look at studies of twins who had been separated at birth and lived in different environments to adulthood. Such studies would separate environmental factors from genetic factors, whereas studies of family members reared in the same household are confounded by the fact that the family members experienced similar environments. If the trait had a strong genetic component, we would expect identical twins reared apart to be similarly taciturn or similarly intelligent. One would have to devise some objective measure of these traits—degrees of being taciturn or smart. Section 1.2 *21. Genetics is said to be both a very old science and a very young science. Explain what is meant by this statement.

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    Chapter One: Introduction to Genetics 7 Solution: Genetics is old in the sense that humans have been aware of hereditary principles for thousands of years and have applied them since the beginning of agriculture and the domestication of plants and animals. It is very young in the sense that the fundamental principles were not uncovered until Mendel’s time, and the discovery of the structure of DNA and the principles of recombinant DNA have occurred within the last 60 years. *22. Match the description ( a through d ) with the correct theory or concept listed below. Preformationism Pangenesis Germ-plasm theory Inheritance of acquired characteristics a. Each reproductive cell contains a complete set of genetic information. Solution: Germ-plasm theory b. All traits are inherited from one parent. Solution: Preformationism c. Genetic information may be altered by use of a characteristic. Solution: Inheritance of acquired characteristics d. Cells of different tissues contain different genetic information. Solution: Pangenesis *23. Compare and contrast the following ideas about inheritance. a. Pangenesis and germ-plasm theory Solution: Pangenesis theorizes that units of genetic information (pangenes) from all parts of the body are carried through the reproductive organs to the embryo where each unit directs the formation of its own specific part of the body. According to the germ- plasm theory, the germ-line tissue or gamete producing cells found within the reproductive organs contain the complete set of genetic information that is passed to

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    8 Chapter One: Introduction to Genetics the gametes. Both theories are similar in that each predicts the passage of genetic information occurs through the reproductive organs. b. Preformationism and blending inheritance Solution: Preformationism predicts that the sperm or egg contains a miniature preformed adult called the homunculus. During development, the homunculus would grow to produce the offspring. Only one parent would contribute genetic traits to the offspring. Blending inheritance requires contributions of genetic material from both parents. According to the theory of blending inheritance, genetic contributions from the parents blend to produce the genetic material of the offspring. Once blended, the genetic material could not be separated for future generations. c. The inheritance of acquired characteristics and our modern theory of heredity Solution: The theory of inheritance of acquired characteristics postulates that traits acquired during one’s lifetime alter the genetic material and can be transmitted to offspring. Our modern theory of heredity indicates that offspring inherit genes located on chromosomes from their parents. These chromosomes segregate during meiosis in the germ cells and are passed into the gametes. Section 1.3 *24. Compare and contrast the following terms: a. Eukaryotic and prokaryotic cells Solution: Both cell types have lipid bilayer membranes, DNA genomes, and machinery for DNA replication, transcription, translation, energy metabolism, response to stimuli, growth, and reproduction. Eukaryotic cells have a nucleus containing chromosomal DNA and possess internal membrane-bound organelles. b. Gene and allele Solution: A gene is the basic unit of heredity, which is dictated by the nucleotide sequence, and typically encodes a functional RNA or polypeptide. An allele is a variant form of a gene, arising through mutation. c. Genotype and phenotype

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    Chapter One: Introduction to Genetics 9 Solution: The genotype is the set of genes or alleles an organism has inherited from its parent(s). The expression of the genes of a particular genotype, through interaction with environmental factors, produces the phenotype, the observable trait. d. DNA and RNA Solution: Both are nucleic acid polymers. RNA contains ribose, whereas DNA contains deoxyribose. RNA also contains uracil as one of the four bases, whereas DNA contains thymine. The other three bases are common to both DNA and RNA. Finally, DNA is usually double-stranded, consisting of two complementary strands and very little secondary structure, whereas RNA is single-stranded with regions of internal base-pairing to form complex secondary structures. e. DNA and chromosome Solution: Chromosomes are structures formed of DNA and associated proteins. The nucleotide sequence of the DNA contains the genetic information. CHALLENGE QUESTIONS *25. The type of albinism that arises with high frequency among Hopi Native Americans (discussed in the introduction to this chapter) is most likely oculocutaneous albinism type II, due to a defect in the OCA2 gene on chromosome 15. Do some research on the Internet to determine how the phenotype of this type of albinism differs from phenotypes of other forms of albinism in humans and the mutated genes that result in these phenotypes. Hint: Visit the Online Mendelian Inheritance in Man Web site (http://www.ncbi.nlm.nih.gov/omim/) and search the database for albinism. Solution: Type of albinism Phenotype Gene mutated OCA2 Pigment reduced in skin, hair, and eyes, but small amount of pigment acquired with age; visual problems OCA2 OCA1B General absence of pigment in hair, skin, and eyes, but may be small amount of pigment; does not vary with age; visual problems Tyrosinase OCA1A Complete absence of pigment; visual problems Tyrosinase OCA3 Some pigment present, but sun sensitivity and visual problems Tyrosinase-related protein 1 OASD Lack of pigment in the eyes and deafness later in life Unknown OA1 Lack of pigment in the eyes but normal elsewhere GPR143 gene, G protein-coupled

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    10 Chapter One: Introduction to Genetics receptor ROCA Bright copper red coloration in skin and hair of Africans; dilution of color in iris Tyrosinase-related protein 1 OCA4 Reduced pigmentation MATP gene, membrane- associated transporter protein. Section 1.1 26. We now know a great deal about the genetics of humans, and humans are the focus of many genetic studies. Should humans be considered a model genetic organism? Why or why not? Solution: Humans are intensively interested in how humans function biologically. Because of this intense interest, we know more about human anatomy, physiology, genetics, and biochemistry than we know about many other organisms. Many human diseases and disorders are associated with human genes. Understanding how to treat and diagnose these diseases and disorders requires intensive studies to identify the gene(s) responsible for the disorder as well as understanding how they are inherited and expressed. Recent advances in the understanding of genetic risk factors associated with diseases such as heart disease and cancer have enabled the development of predictive genetic tests for some of these disorders. These successes continue to stimulate a focus in identifying genetic risk factors for other diseases. The ability of families to keep careful records about members extending back many generations has facilitated the study of human inheritance aiding the ability of researchers to identify genetic markers within families. In addition, these detailed records have provided some humans who are intensely interested in their own heredity the ability to trace their ancestry. Section 1.3 *27. Suppose that life exists elsewhere in the universe. All life must contain some type of genetic information, but alien genomes might not consist of nucleic acids and have the same features as those found in the genomes of life on Earth. What might be the common features of all genomes, no matter where they exist? Solution: All genomes must have the ability to store complex information, the capacity to vary and yet be transmissible in large part faithfully to subsequent generations. The blueprint for the entire organism must be contained within the genome of each reproductive cell. The information has to be in the form of a code that can be used as a set of instructions for assembling the components of the cells. The genetic material of any organism must be stable, be replicated precisely, and be transmitted faithfully to the progeny, but must be capable of mutating.

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    Chapter One: Introduction to Genetics 11 28. Choose one of the ethical or social issues in parts a through e and give your opinion on the issue. For background information, you might read one of the articles on ethics marked with an asterisk in the Suggested Readings section for Chapter 1 at http://courses.bfwpub.com/pierce5e. a. Should a person’s genetic makeup be used in determining his or her eligibility for life insurance? Solution: Arguments pro: Genetic susceptibility to certain types of diseases or conditions is relevant information regarding consequences of exposure to certain occupational hazards. Genes that will result in neurodegenerative diseases, such as Huntington disease, Alzheimer disease, or breast cancer, could logically be considered preexisting conditions. Insurance companies have a right, and arguably a duty to their customers, to exclude people with genetic preconditions so that insurance rates can be lowered for the general population. Arguments con: The whole idea of insurance is to spread the risk and pool assets. Excluding people based on their genetic makeup would deny insurance to people who need it most. Indeed, as information about various genetic risks accumulates, more people would become excluded until only a small fraction of the population is insurable. Further, many genes are incompletely penetrant and variably expressed. Not all women who have mutant BRCA1 or BRCA2 genes develop breast cancer. And some women who have breast cancer lack mutations in those genes. b. Should biotechnology companies be able to patent newly sequenced genes? Solution: Pro: Patenting genes provides companies with protection for their investment in research and development of new drugs and therapies. Without such patent protection, companies would have less incentive to expend large amounts of money in genetic research and thus would slow the pace of advancement of medical research. Such a result would be detrimental to everyone. Con: Patents on human genes would be like allowing companies to patent a human arm. Genes are integral parts of our selves, so how can a company patent something that every human has? c. Should gene therapy be used on people? Solution: Pro: Gene therapy can be used to cure previously incurable or intractable genetic disorders and to relieve the suffering of millions of people. Con: Gene therapy may lead to genetic engineering of people for unsavory ends. Who determines what is a genetic defect? Is short stature a genetic defect? Should genetic testing be made available for inherited conditions for which there is no treatment or cure?

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    12 Chapter One: Introduction to Genetics d. Should genetic testing be made available for inherited disorders for which there is no treatment or cure? Solution: Pro: Information will provide relief from unnecessary anxiety (if the test is negative). Even if the test result is positive for a genetic disorder, it provides the individual, the family, and friends with information and time to prepare. Information about one’s own genetic makeup is a right; every person should be able to make his or her own choice as to whether he or she wants this information. Con: If there is no treatment or cure, a positive test result can have no good consequences. It’s like receiving a death sentence or sentence of extended punishment. It will only engender feelings of hopelessness and depression and may cause some people to terminate their own lives prematurely. 29. A 45-year old woman undergoes genetic testing and discovers that she is at high risk for developing colon cancer and Alzheimer disease. Because her children have 50% of her genes, they also may be at an increased risk for these diseases. Does she have a moral or legal obligation to tell her children and other close relatives about the results of her genetic testing? Solution: Legally, she is not required to inform her children or other relatives about her test results, but people may have different opinions about her moral and parental responsibilities. On the one hand, she has the legal right to keep private the results of any medical information, including the results of genetic testing. On the other hand, her children may be at increased risk of developing these disorders and might benefit from that knowledge. For example, the risk of colon cancer can be reduced by regular exams, so that any tumors can be detected and removed before they become cancerous. Some people might argue that her parental responsibilities include providing her children with information about possible medical problems. Another issue to consider is the possibility that her children or other relatives might not want to know their genetic risk, particularly for a disorder like Alzheimer for which there is no cure. 30. Suppose that you could undergo genetic testing at age 18 for susceptibility to a genetic disease that would not appear until middle age and has no available treatment. a. What would be some of the possible reasons for having such a genetic test and some of the possible reasons for not having the test? Solution: Having the genetic test removes doubt about the potential for the disorder—either you are susceptible or not. By knowing about the potential of a genetic disorder lifestyle changes could possibly be made to lessen the impact of the disease or lessen the risk. The types and nature of future medical tests could be positively impacted by the

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    Chapter One: Introduction to Genetics 13 genetic testing, thus allowing for early warning and screening for the disease. The knowledge could also have impact on future family plans and allow for informed decisions regarding future offspring and the potential of passing the trait to your offspring. Also by knowing the future, one could plan one’s life accordingly. Reasons for not having the test typically revolve around the potential for testing positive for the susceptibility to the genetic disease. If the susceptibility was detected, the potential for discrimination could exist. For example, your employer (or possibly future employer) might see you as a long-term liability, thus affecting employment options. Insurance companies may not want to insure you for that condition or symptoms of the disorder, and potentially social stigmatism associated with the disease could be a factor. Knowledge of the potential future condition could lead to psychological difficulties in coping with the anxiety of waiting for the disease to manifest. b. Would you personally want to be tested? Explain your reasoning. Solution: There is no “correct” answer, but for me, yes, I would personally want to be tested. The test would remove doubt about the susceptibility particularly if the genetic disease had been demonstrated to occur in my family. Either a positive or negative result would allow for informed planning of lifestyle, medical testing, and family choices in the future.

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    Chapter Two: Chromosomes and Cellular Reproduction COMPREHENSION QUESTIONS Section 2.1 1. What are some genetic differences between prokaryotic and eukaryotic cells? Solution: Prokaryotic cell Eukaryotic cell No nucleus No paired chromosomes (haploid) Typically single circular chromosome containing a single origin of replication Single chromosome is replicated with each copy moving to opposite sides of the cell No histone proteins bound to DNA Nucleus present Paired chromosomes common (diploid) Typically multiple linear chromosomes containing centromeres, telomeres, and multiple origins of replication Chromosomes are replicated and segregate during mitosis or meiosis to the proper location Histone proteins are bound to DNA 2. Why are the viruses that infect mammalian cells useful for studying the genetics of mammals? Solution: It is thought that viruses must have evolved after their host cells because a host is required for viral reproduction. Viral genomes are closely related to their host genomes. The close relationship between a mammalian virus and its mammalian cell host, along with the simpler structure of the viral particle, makes it useful in studying the genetics of mammals. The viral genome will have a similar structure to the mammalian cell host, but because it has fewer genes, it will be easier to decipher the interactions and regulation of the viral genes. Section 2.2 3. List three fundamental events that must take place in cell reproduction. Solution: (1) A cell’s genetic information must be copied. (2) The copies of the genetic information must be separated from one another. (3) The cell must divide into two daughter cells. 4. Outline the process by which prokaryotic cells reproduce.

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    Chapter Two: Chromosomes and Cellular Reproduction 15 Solution: (1) Replication of the circular chromosome takes place . (2) The two replicated chromosomal copies attach to the plasma membrane. (3) The plasma membrane grows, which results in the separation of the two chromosomes. (4) A new cell wall is formed between the two chromosomes, producing two cells, each with its own chromosome. 5. Name three essential structural elements of a functional eukaryotic chromosome and describe their functions. Solution: (1) Centromere: serves as the point of attachment for the kinetochore to which spindle fibers (microtubules) attach (2) Telomeres, or the natural ends of the linear eukaryotic chromosome: serve to stabilize the ends of the chromosome; may have a role in limiting cell division (3) Origins of replication: serve as the starting place for DNA synthesis 6. Sketch and identify four different types of chromosomes based on the position of the centromere. Solution: metacentric submetacentric acrocentric telocentric 7. List the stages of interphase and the major events that take place in each stage. Solution: Three predominant stages are found in interphase of cells active in the cell cycle. (1) G 1 (Gap 1): In this phase, the cell grows and synthesizes proteins necessary for cell division. During G 1 , the G 1 /S checkpoint takes place. Once the cell has passed this checkpoint, it is committed to divide. (2) S phase: During S phase, DNA replication takes place. (3) G 2 (Gap 2): In G 2 , additional biochemical reactions take place that prepare the cell for mitosis. A major checkpoint in G 2 is the G 2 /M checkpoint. Once the cell has passed this checkpoint, it enters into mitosis. A fourth stage is frequently found in cells prior to the G 1 /S checkpoint. Cells may exit the active cell cycle and enter into a nondividing stage called G 0 . 8. What are checkpoints? List some of the important checkpoints in the cell cycle.

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