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All Textbook Solutions for Human Heredity: Principles and Issues (MindTap Course List)

Ancient societies used knowledge that traits are heritable in domesticating animals and developing agricultural crops. What might account for the failure to recognize that the same processes operate in humans?Why do unrelated children with a disorder such as Down syndrome resemble each other more closely than they do their siblings?Mary and Marcie. identical twins, go to the same internist who is also a faculty member at a major medical center. At their last visit, they each received a brochure describing a genetics research program recently launched by the hospital and its affiliated university. Researchers were asking for volunteers to fill out a questionnaire and a consent form, donate a blood sample, and have their medical records encoded and transferred to a database. The goal was to enroll 100,000 participants, and the brochure noted that over 10,000 people had already agreed to participate. The blood sample would be used to extract DNA. which would be encoded with the same number as the medical records. This DNA would be used to search for genes associated with conditions such as arthritis, diabetes, and Alzheimer disease. The idea is that researchers interested in studying arthritis would use the medical records to identify which participants have the condition and then use DNA from those individuals to find genetic similarities that are not present in participants who do not have arthritis. The genetic similarities help identify regions of the genome that contain genes associated with arthritis. These regions can then be studied in detail to identify and isolate genes that may be associated with arthritis and other inflammatory disorders. In exchange for enrolling, participants would be informed about any genetic conditions or predispositions to genetic disease they carry and would receive free access to testing. After discussing the brochure. Mary decided to enroll, but Marcie decided she did not want to do so. She said she did not want to know what diseases she may develop or which disease genes she may carry. At their next annual visit. Marys internist told her that because her questionnaire indicated that some relatives had Alzheimer disease, her DNA was used in a study to identify risk genes. He said she had been identified as a carrier of a gene that greatly increased the likelihood that she would develop Alzheimer disease. The physician told her that age was the greatest risk factor, and while it was not 100% certain she would become a victim of Alzheimer disease, the gene she carries is a factor in 2025% of all cases. Mary asked if there was anything she could do about these findings. The internist told her that exercise, controlling blood pressure and cholesterol levels, as well as participating in mentally challenging activities such as reading or playing a musical instrument may all help reduce her chances of developing this disease. Mary then asked if Marcie was going to be told about Marys genetic risk, and the internist said that he would not tell her. For the next few days. Mary was conflicted about the situation. Marcie was an Identical twin, and If Mary carried a gene predisposing her to Alzheimer disease. Marcie must carry the same gene. Marcie did not exercise with Mary, had high blood pressure, and little interest in reading or social activities. Mary did not know whether she should tell Marcie. If you were advising Mary, what would you say? Should she tell Marcie about the risk? Should she not tell her, but instead try to get Marcie to exercise and be more social? Should Mary ask their internist to talk with Marcie about this?Summarize Mendels conclusions about traits and how they are passed from generation to generation.What is population genetics?What is hereditarianism, and what is the invalid assumption it makes?What impact has recombinant DNA technology had on genetics and society?5QP6QPIn what way has biotechnology had an impact on agriculture in the United States?We each carry 20,000 genes in our genome. Genes can be patented, and over 6,000 human genes have been patented. Do you think that companies or individuals should be able to patent human genes? Why or why not?If your father were diagnosed with an inherited disease that develops around the age of 50, would you want to be tested to find out whether you would develop this disease? If so, when would you want to be tested? As a teenager or sometime in your 40s? If not, would you have children?1CS2CS3CSCell Structure Reflects Function What advantages are there in having the interior of the cell divided into a number of compartments such as the nucleus, the ER, lysosomes, and so forth?Assign a function(s) to the following cellular structures: a. plasma membrane b. mitochondrion c. nucleus d. ribosomeHow many autosomes are present in a body cell of a human being? In a gamete?Define the following terms: a. chromosome b. chromatinHuman haploid gametes (sperm and eggs) contain: a. 46 chromosomes, 46 chromatids b. 46 chromosomes, 23 chromatids c. 23 chromosomes, 46 chromatids d. 23 chromosomes, 23 chromatids6QP7QPIn the cell cycle, at which stages do two chromatids make up one chromosome? a. beginning of mitosis b. end of G1 c. beginning of S d. end of mitosis e. beginning of G2Does the cell cycle refer to mitosis as well as meiosis?It is possible that an alternative mechanism for generating germ cells could have evolved. Consider meiosis in a germ cell precursor (a cell that is diploid but will go on to make gametes). If the S phase were skipped, which meiotic division (meiosis I or meiosis II) would no longer be required?Identify the stages of mitosis, and describe the important events that occur during each stage.Why is cell furrowing important in cell division? If cytokinesis did not occur, what would be the end result?A cell from a human female has just undergone mitosis. For unknown reasons, the centromere of chromosome 7 failed to divide. Describe the chromosomal contents of the daughter cells.During which phases of the mitotic cycle would the terms chromosome and chromatid refer to identical structures?Describe the critical events of mitosis that are responsible for ensuring that each daughter cell receives a full set of chromosomes from the parent cell.Mitosis occurs daily in a human being. What type of cells do humans need to produce in large quantities on a daily basis?Speculate on how the Hayflick limit may lead to genetic disorders such as progeria and Werner syndrome. How is this related to cell division?How can errors in the cell cycle lead to cancer in humans?List the differences between mitosis and meiosis in the following chart:In the following diagram, designate each daughter cell as diploid (2n) or haploid (n).Which of the following statements is not true in comparing mitosis and meiosis? a. Twice the number of cells are produced in meiosis as in mitosis. b. Meiosis is involved in the production of gametes, unlike mitosis. c. Crossing over occurs in meiosis I but not in meiosis II or mitosis. d. Meiosis and mitosis both produce cells that are genetically identical. e. In both mitosis and meiosis, the parental cell is diploid.Match the phase of cell division with the following diagrams. In these cells, 2n = 4. a. anaphase of meiosis I b. interphase of mitosis c. metaphase of mitosis d. metaphase of meiosis I e. metaphase of meiosis IIA cell has a diploid number of 6 (2n = 6). a. Draw the cell in metaphase of meiosis I. b. Draw the cell in metaphase of mitosis. c. How many chromosomes are present in a daughter cell after meiosis I? d. How many chromatids are present in a daughter cell after meiosis II? e. How many chromosomes are present in a daughter cell after mitosis? f. How many pairs of homologous chromosomes are visible in the cell in metaphase of meiosis I?A cell (2n = 4) has undergone cell division. Daughter cells have the following chromosome content. Has this cell undergone mitosis, meiosis I, or meiosis II?We are following the progress of human chromosome 1 during meiosis. At the end of prophase I, how many chromosomes, chromatids, and centromeres are present to ensure that chromosome 1 faithfully traverses meiosis?What is physically exchanged during crossing over?Compare meiotic anaphase I with meiotic anaphase II. Which meiotic anaphase is most similar to the mitotic anaphase?Provide two reasons why meiosis leads to genetic variation in diploid organisms.Why do scientists design experiments to disprove the hypothesis they are testing instead of trying to prove that the hypothesis is correct?Should Ockhams razor be considered an irrefutable principle of logic or a practical guideline? Why?1EGFor most cases, a p value of 0.05 is used to determine whether results fit expected values. Is this a magic number, or could p values be set more stringently, say 0.01, or more lax, say 0.10? What effect would these values have on the reliability of the chi-square test?1CS2CS3CS1QPCrossing Pea Plants: Mendels Study of Single Traits Of the following, which are phenotypes and which are genotypes? a. Aa b. tall plants c. BB d. abnormal cell shape e. AaBbCrossing Pea Plants: Mendels Study of Single Traits Define Mendels Law of Segregation.4QPCrossing Pea Plants: Mendels Study of Single Traits Suppose that organisms have the following genotypes. What types of gametes will these organisms produce, and in what proportions? a. Aa b. AA c. aa6QPCrossing Pea Plants: Mendels Study of Single Traits Wet ear wax (W) is dominant over dry ear wax (w). a. A 3 : 1 phenotypic ratio of F1 progeny indicates that the parents are of what genotype? b. A 1 : 1 phenotypic ratio of F1 progeny indicates that the parents are of what genotype?Crossing Pea Plants: Mendels Study of Single Traits An unspecified characteristic controlled by a single gene is examined in pea plants. Only two phenotypic states exist for this trait. One phenotypic state is completely dominant to the other. A heterozygous plant is self-crossed. What proportion of the progeny of plants exhibiting the dominant phenotype is homozygous?Crossing Pea Plants: Mendels Study of Single Traits Sickle cell anemia (SCA) is a human genetic disorder caused by a recessive allele. A couple plan to marry and want to know the probability that they will have an affected child. With your knowledge of Mendelian inheritance, what can you tell them if (1) each has one affected parent and a parent with no family history of SCA or (2) the man is affected by the disorder but the woman has no family history of SCA?Crossing Pea Plants: Mendels Study of Single Traits If you are informed that tune deafness is a heritable trait, and that a tune deaf couple is expecting a child, can you conclude that the child will be tune deaf?Crossing Pea Plants: Mendels Study of Single Traits Stem length in pea plants is controlled by a single gene. Consider the cross of a true-breeding long-stemmed variety to a true-breeding short-stemmed variety in which long stems are completely dominant. a. If 120 F1 plants are examined, how many plants are expected to be long stemmed? Short stemmed? b. Assign genotypes to both P1 varieties and to all phenotypes listed in (a). c. A long-stemmed F1 plant is self-crossed. Of 300 F2 plants, how many should be long stemmed? Short stemmed? d. For the F2 plants mentioned in (c), what is the expected genotypic ratio?More Crosses with Pea Plants: The Principle of Independent Assortment Organisms have the following genotypes. What types of gametes will these organisms produce, and in what proportions? a. Aabb b. AABb c. AaBbMore Crosses with Pea Plants: The Principle of Independent Assortment Given the following matings, what are the predicted phenotypic ratios of the offspring? a. AABb Aabb b. AaBb aabb c. AaBb AaBb14QPMore Crosses with Pea Plants: The Principle of Independent Assortment Two traits are examined simultaneously in a cross of two pure-breeding pea-plant varieties. Pod shape can be either swollen or pinched. Pea color can be either green or yellow. A plant with the traits swollen and green is crossed with a plant with the traits pinched and yellow, and a resulting F1 plant is self-crossed. A total of 640 F2 progeny are phenotypically categorized as follows: 360 swollen yellow 120 swollen green 120 pinched yellow 40 pinched green a. What is the phenotypic ratio observed for pod shape? Pea color? b. What is the phenotypic ratio observed for both traits considered together? c. What is the dominance relationship for pod shape? Pea color? d. Deduce the genotypes of the P1 and F1 generations.More Crosses with Pea Plants: The Principle of Independent Assortment Consider the following cross in pea plants, in which smooth pea shape is dominant to wrinkled, and yellow pea color is dominant to green. A plant with smooth yellow peas is crossed to a plant with wrinkled green peas. The offspring produced peas that were all smooth and yellow. What are the genotypes of the parents? What are the genotypes of the offspring?17QPMore Crosses with Pea Plants: The Principle of Independent Assortment Determine the possible genotypes of the following parents by analyzing the phenotypes of their children. In this case, we will assume that brown eyes (B) is dominant to blue (b) and that right-handedness (R) is dominant to left-handedness (r). a. Parents: brown eyes, right-handed brown eyes, right-handed Offspring: 3/4 brown eyes, right-handed 1/4 blue eyes, right-handed b. Parents: brown eyes, right-handed blue eyes, right-handed Offspring: 6/16 blue eyes, right-handed 2/16 blue eyes, left-handed 6/16 brown eyes, right-handed 2/16 brown eyes, left-handed c. Parents: brown eyes, right-handed blue eyes, left-handed Offspring: 1/4 brown eyes, right-handed 1/4 brown eyes, left-handed 1/4 blue eyes, right-handed 1/4 blue eyes, left-handedMore Crosses with Pea Plants: The Principle of Independent Assortment Think about this one carefully. Albinism and hair color are governed by different genes. A recessively inherited form of albinism causes affected individuals to lack pigment in their skin, hair, and eyes. In hair color, red hair is inherited as a recessive trait and brown hair is inherited as a dominant trait relative to red hair. An albino woman whose parents both have red hair has two children with a man who is normally pigmented and has brown hair. The brown-haired partner has one parent who has red hair. The first child is normally pigmented and has brown hair. The second child is albino. a. What is the hair color (phenotype) of the albino parent? b. What is the genotype of the albino parent for hair color? c. What is the genotype of the brown-haired parent with respect to hair color? Skin pigmentation? d. What is the genotype of the first child with respect to hair color and skin pigmentation? e. What are the possible genotypes of the second child for hair color? What is the phenotype of the second child for hair color? Can you explain this?More Crosses with Pea Plants: The Principle of Independent Assortment Consider the following cross: P1: AABBCCDDEE aabbccddee F1: AaBbCcDdEe (self-cross to get F2) What is the chance of getting an AaBBccDdee individual in the F2 generation?More Crosses with Pea Plants: The Principle of Independent Assortment In the following trihybrid cross, determine the chance that an individual could be phenotypically A, b, C in the F1 generation. P1: AaBbCc AabbCCMore Crosses with Pea Plants: The Principle of Independent Assortment In pea plants, long stems are dominant to short stems, purple flowers are dominant to white, and round peas are dominant to wrinkled. Each trait is determined by a single, different gene. A plant that is heterozygous at all three loci is self-crossed, and 2,048 progeny are examined. How many of these plants would you expect to be long stemmed with purple flowers, producing wrinkled peas?Meiosis Explains Mendels Results: Genes Are on Chromosomes Discuss the pertinent features of meiosis that provide a physical correlate to Mendels abstract genetic laws of random segregation and independent assortment.Meiosis Explains Mendels Results: Genes Are on Chromosomes The following diagram shows a hypothetical diploid cell. The recessive allele for albinism is represented by a, and d represents the recessive allele for deafness. The normal alleles for these conditions are represented by A and D, respectively. a. According to the principle of segregation, what is segregating in this cell? b. According to Mendels principle of independent assortment, what is independently assorting in this cell? c. How many chromatids are in this cell? d. Write the genotype of the individual from whom this cell was taken. e. What is the phenotype of this individual? f. What stage of cell division is represented by this cell (prophase, metaphase, anaphase, or telophase of meiosis I, meiosis II, or mitosis)? g. After meiosis is complete, how many chromatids and chromosomes will be present in one of the four progeny cells?Meiosis Explains Mendels Results: Genes Are on Chromosomes Define the following pedigree symbols:26QP27QPVariations on a Theme by Mendel A characteristic of snapdragons amenable to genetic analysis is flower color. Imagine that a true-breeding red- flowered variety is crossed to a pure line having white flowers. The progeny are exclusively pink-flowered. Diagram this cross, including genotypes for all P1 and F1 phenotypes. What is the mode of inheritance? Let F = red and f = white.29QPVariations on a Theme by Mendel Pea plants usually have white or red flowers. A strange pea-plant variant is found that has pink flowers. A selfcross of this plant yields the following phenotypes: 30 red flowers 62 pink flowers 33 white flowers What are the genotypes of the parents? What is the genotype of the progeny with red flowers?31QP32QP33QP34QP35QP36QPDoes a pedigree drawn from the available information offer strong support for the idea that Noah was homozygous for the recessive trait albinism? What other information about later generations would you like to have?2EGDid the fact that Prince Albert and Queen Victoria were first cousins have anything to do with the fact that she carried the allele for hemophilia? Why or why not?Which members of the pedigree could have been carriers, and which might have been the source of the mutation?Pedigree analysis is a fundamental tool for investigating whether or not a trait is following a Mendelian pattern of inheritance. It can also be used to help identify individuals within a family who may be at risk for the trait. Adam and Sarah, a young couple of Eastern European Jewish ancestry, went to a genetic counselor because they were planning a family and wanted to know what their chances were for having a child with a genetic condition. The genetic counselor took a detailed family history from both of them and discovered several traits in their respective families. Sarahs maternal family history is suggestive of an autosomal dominant pattern of cancer predisposition to breast and ovarian cancer because of the young ages at which her mother and grandmother were diagnosed with their cancers. If a mutant allele that predisposed to breast and ovarian cancer was inherited in Sarahs family, she, her sister, and any of her own future children could be at risk for inheriting this mutation. The counselor told her that genetic testing is available that may help determine if this mutant allele is present in her family members. Adams paternal family history has a very strong pattern of early onset heart disease. An autosomal dominant condition known as familial hypercholesterolemia may be responsible for the large number of deaths from heart disease. As with hereditary breast and ovarian cancer, genetic testing is available to see if Adam carries the mutant allele. Testing will give the couple more information about the chances that their children could inherit this mutation. Adam had a first cousin who died from Tay-Sachs disease (TSD), a fatal autosomal recessive condition most commonly found in people of Eastern European Jewish descent. Because TSD is a recessively inherited disorder, both of his cousins parents must have been heterozygous carriers of the mutant allele. If that is the case, Adams father could be a carrier as well. If Adams father carries the mutant TSD allele, it is possible that Adam inherited this mutation. Because Sarah is also of Eastern European Jewish ancestry, she could also be a carrier of the gene, even though no one in her family has been affected with TSD. If Adam and Sarah are both carriers, each of their children would have a 25% chance of being afflicted with TSD. A simple blood test performed on both Sarah and Adam could determine whether they are carriers of this mutation. If Sarah carries the mutant cancer allele and Adam carries the mutant heart disease allele, what is the chance that they would have a child who is free of both diseases? Are these good odds?Pedigree analysis is a fundamental tool for investigating whether or not a trait is following a Mendelian pattern of inheritance. It can also be used to help identify individuals within a family who may be at risk for the trait. Adam and Sarah, a young couple of Eastern European Jewish ancestry, went to a genetic counselor because they were planning a family and wanted to know what their chances were for having a child with a genetic condition. The genetic counselor took a detailed family history from both of them and discovered several traits in their respective families. Sarahs maternal family history is suggestive of an autosomal dominant pattern of cancer predisposition to breast and ovarian cancer because of the young ages at which her mother and grandmother were diagnosed with their cancers. If a mutant allele that predisposed to breast and ovarian cancer was inherited in Sarahs family, she, her sister, and any of her own future children could be at risk for inheriting this mutation. The counselor told her that genetic testing is available that may help determine if this mutant allele is present in her family members. Adams paternal family history has a very strong pattern of early onset heart disease. An autosomal dominant condition known as familial hypercholesterolemia may be responsible for the large number of deaths from heart disease. As with hereditary breast and ovarian cancer, genetic testing is available to see if Adam carries the mutant allele. Testing will give the couple more information about the chances that their children could inherit this mutation. Adam had a first cousin who died from Tay-Sachs disease (TSD), a fatal autosomal recessive condition most commonly found in people of Eastern European Jewish descent. Because TSD is a recessively inherited disorder, both of his cousins parents must have been heterozygous carriers of the mutant allele. If that is the case, Adams father could be a carrier as well. If Adams father carries the mutant TSD allele, it is possible that Adam inherited this mutation. Because Sarah is also of Eastern European Jewish ancestry, she could also be a carrier of the gene, even though no one in her family has been affected with TSD. If Adam and Sarah are both carriers, each of their children would have a 25% chance of being afflicted with TSD. A simple blood test performed on both Sarah and Adam could determine whether they are carriers of this mutation. Would you want to know the results of the cancer, heart disease, and TSD tests if you were Sarah and Adam? Is it their responsibility as potential parents to gather this type of information before they decide to have a child?Pedigree analysis is a fundamental tool for investigating whether or not a trait is following a Mendelian pattern of inheritance. It can also be used to help identify individuals within a family who may be at risk for the trait. Adam and Sarah, a young couple of Eastern European Jewish ancestry, went to a genetic counselor because they were planning a family and wanted to know what their chances were for having a child with a genetic condition. The genetic counselor took a detailed family history from both of them and discovered several traits in their respective families. Sarahs maternal family history is suggestive of an autosomal dominant pattern of cancer predisposition to breast and ovarian cancer because of the young ages at which her mother and grandmother were diagnosed with their cancers. If a mutant allele that predisposed to breast and ovarian cancer was inherited in Sarahs family, she, her sister, and any of her own future children could be at risk for inheriting this mutation. The counselor told her that genetic testing is available that may help determine if this mutant allele is present in her family members. Adams paternal family history has a very strong pattern of early onset heart disease. An autosomal dominant condition known as familial hypercholesterolemia may be responsible for the large number of deaths from heart disease. As with hereditary breast and ovarian cancer, genetic testing is available to see if Adam carries the mutant allele. Testing will give the couple more information about the chances that their children could inherit this mutation. Adam had a first cousin who died from Tay-Sachs disease (TSD), a fatal autosomal recessive condition most commonly found in people of Eastern European Jewish descent. Because TSD is a recessively inherited disorder, both of his cousins parents must have been heterozygous carriers of the mutant allele. If that is the case, Adams father could be a carrier as well. If Adams father carries the mutant TSD allele, it is possible that Adam inherited this mutation. Because Sarah is also of Eastern European Jewish ancestry, she could also be a carrier of the gene, even though no one in her family has been affected with TSD. If Adam and Sarah are both carriers, each of their children would have a 25% chance of being afflicted with TSD. A simple blood test performed on both Sarah and Adam could determine whether they are carriers of this mutation. Would you decide to have a child if the test results said that you carry the mutation for breast and ovarian cancer? The heart disease mutation? The TSD mutation? The heart disease and the mutant alleles?Pedigree Analysis Is a Basic Method in Human Genetic: What are the reasons that pedigree charts are used?Pedigree Analysis Is a Basic Method in Human Genetics Pedigree analysis permits all of the following except: a. an orderly presentation of family information b. the determination of whether a trait is genetic c. the determination of whether a trait is dominant or recessive d. an understanding of which gene is involved in a heritable disorder e. the determination of whether a trait is sex-linked or autosomalPedigree Analysis Is a Basic Method in Human Genetics Using the pedigree provided, answer the following questions. a. Is the proband male or female? b. Is the grandfather of the proband affected? c. How many siblings does the proband have, and where is he or she in the birth order?Pedigree Analysis Is a Basic Method in Human Genetic: What does OMIM stand for? What kinds of information are in this database?Analysis of Autosomal Recessive and Dominant Traits a. What pattern of inheritance is suggested by the following pedigree? b. For genotype assignment, assume that the pedigree is for an autosomal dominant trait and that the affected male in the first generation is heterozygous. Assign genotypes to all other individuals in the pedigree.Analysis of Autosomal Recessive and Dominant Traits Does the indicated individual (III-5) show the trait in question?Use the following information to respond to the three questions posed below: (1) The proband (affected individual who led to the construction of the pedigree) exhibits the trait. (2) Neither her husband nor her only sibling, an older brother, exhibits the trait. (3) The proband has five children by her current husband. The oldest is a boy, followed by a girl, then another boy, and then identical twin girls. Only the second oldest fails to exhibit the trait. (4) Both parents of the proband show the trait. a. Construct a pedigree of the trait in this family. b. Determine how the trait is inherited (go step by step to examine each possible pattern of inheritance). c. Can you deduce the genotype of the probands husband for this trait?Analysis of Autosomal Recessive and Dominant Traits In the following pedigree, assume that the father of the proband is homozygous for a rare trait. What pattern of inheritance is consistent with this pedigree? In particular, explain the phenotype of the proband.Analysis of Autosomal Recessive and Dominant Traits Using the following pedigree, deduce a compatible pattern of inheritance. Identify the genotype of the individual in question.A proband female with an unidentified disease seeks the advice of a genetic counselor before starting a family. Based on the following data, the counselor constructs a pedigree encompassing three generations: (1) The maternal grandfather of the proband has the disease. (2) The mother of the proband is unaffected and is the youngest of five children, the three oldest being male. (3) The proband has an affected older sister, but the youngest siblings are unaffected twins (boy and girl). (4) All the individuals who have the disease have been revealed. Duplicate the counselors featAnalysis of Autosomal Recessive and Dominant Traits Describe the primary gene or protein defect and the resulting phenotype for the following diseases: a. cystic fibrosis b. Marfan syndrome12QPAnalysis of Autosomal Recessive and Dominant Traits The father of 12 children begins to show symptoms of Huntington disease. a. What is the probability that Sam, the mans second-oldest son (II-2), will suffer from the disease if he lives a normal life span? (Sams mother and her ancestors do not have the disease.) b. Can you infer anything about the presence of the disease in Sams paternal grandparents?Analysis of Autosomal Recessive and Dominant Traits Huntington disease is a rare, fatal disease that usually develops in the fourth or fifth decade of life. It is caused by a single autosomal dominant allele. A phenotypically normal man in his twenties who has a 2-year-old son of his own learns that his father has developed Huntington disease. What is the probability that he himself will develop the disease? What is the chance that his young son will eventually develop the disease?Analysis of X-Linked Dominant and Recessive Traits The X and Y chromosomes are structurally and genetically distinct. However, they do pair during meiosis at a small region near the tips of their short arms, indicating that the chromosomes are homologous in this region. If a gene lies in this region, will its pattern of transmission be more like that of a sex-linked gene or an autosomal gene? Why?16QPAnalysis of X-Linked Dominant and Recessive Traits A young boy is color-blind. His one brother and five sisters are not. The boy has three maternal uncles and four maternal aunts. None of his uncles children or grandchildren is color-blind. One of the maternal aunts married a color-blind man, and half of her children, both male and female, are color-blind. The other aunts married men who have normal color vision. All their daughters have normal vision, but half of their sons are color-blind. a. Which of the boys four grandparents transmitted the gene for color blindness? b. Are any of the boys aunts or uncles color-blind? c. Is either of the boys parents color-blind?Analysis of Autosomal Recessive and Dominant Traits Describe the phenotype and primary gene or protein defect of the X-linked recessive disease muscular dystrophy.Analysis of X-Linked Dominant and Recessive Traits Suppose a couple, both phenotypically normal, have two children: one unaffected daughter and one son affected with a genetic disorder. The phenotype ratio is 1:1, making it difficult to determine whether the trait is autosomal or X-linked. With your knowledge of genetics, what are the genotypes of the parents and children in the autosomal case? In the X-linked case?Analysis of X-Linked Dominant and Recessive Traits The following is a pedigree for a common genetic trait. Analyze the pedigree to determine whether the trait is inherited as: a. autosomal dominant b. autosomal recessive c. X-linked dominant d. X-linked recessive e. Y-linkedAnalysis of X-Linked Dominant and Recessive Traits As a genetic counselor investigating a genetic disorder in a family, you are able to collect a four-generation pedigree that details the inheritance of the disorder in question. Analyze the information in the pedigree to determine whether the trait is inherited as: a. autosomal dominant b. autosomal recessive c. X-linked dominant d. X-linked recessive e. Y-linkedAnalysis of X-Linked Dominant and Recessive Traits In the eighteenth century, a young boy with a skin condition known as ichthyosis hystrix gravior was identified. The phenotype of this disorder includes thickening of skin and the formation of loose spines that are sloughed off periodically. This man married and had six sons, all of whom had the same condition. He also had several daughters, all of whom were unaffected. In all succeeding generations, the condition was passed on from father to son. What can you theorize about the location of the gene that causes ichthyosis hystrix gravior?23QP24QPVariations in Phenotype Expression Define penetrance and expressivity.26QPVariations in Phenotype Expression A genetic disorder characterized by falling asleep in genetics lectures is known to be 20% penetrant. All 90 students in a genetics class are homozygous for this gene. Theoretically, how many of the 90 students will fall asleep during the next lecture?Variations in Phenotype Expression Explain how camptodactyly is an example of expressivity.1GRWhat are the possible advantages or disadvantages to the organism or its offspring resulting from DNA modification by environmental factors?After hearing this information, should Sue and Tim feel that their chances of having a child with a cleft lip are increased over that of the general population? Sue and Tim were referred for genetic counseling after they inquired about the risk of having a child with a cleft lip. Tim was born with a mild cleft lip that was surgically repaired. He expressed concern that his future children could be at risk for a more severe form of clefting. Sue was in her 12th week of pregnancy, and both were anxious about the pregnancy because Sue had had a difficult time conceiving. The couple stated that they would not consider terminating the pregnancy for any reason but wanted to be prepared for the possibility of having a child with a birth defect. The genetic counselor took a three-generation family history from both Sue and Tim and found that Tim was the only person to have had a cleft lip. Sues family history showed no cases of cleft lip. Tim and Sue had several misconceptions about clefting, and the genetic counselor spent time explaining how cleft lips occur and some of the known causes of this birth defect. The following list summarizes the counselors discussion with the couple. Fathers, as well as mothers, can pass on genes that cause clefting. Some clefts are caused by environmental factors, meaning that the condition didnt come from the father or the mother. One child in 33 is born with some sort of birth defect. One in 700 is born with a cleft-related birth defect. Most clefts occur in boys; however, a girl can be born with a cleft. If a person (male or female) is born with a cleft, the chances of that person having a child with a cleft, given no other obvious factor, is 7 in 100. Some clefts are related to identifiable syndromes. Of those, some are autosomal dominant. A person with an autosomal dominant gene has a 50% probability of passing the gene to an offspring. Many clefts run in families even when there does not seem to be any identifiable syndrome present. Clefting seems to be related to ethnicity, occurring most often among Asians, Latinos, and Native Americans (1 : 500); next most often among persons of European ethnicity (1 : 700); and least often among persons of African origin (1 : 1,000). A cleft condition develops during the fourth to the eighth week of pregnancy. After that critical period, nothing the mother does can cause a cleft. Sometimes a cleft develops even before the mother is aware that she is pregnant. Women who smoke are twice as likely to give birth to a child with a cleft. Women who ingest large quantities of vitamin A or low quantities of folic acid are more likely to have children with a cleft. In about 70% of cases, the fetal face is clearly visible using ultrasound. Facial disorders have been detected at the 15th gestational week of pregnancy. Ultrasound can be precise and reliable in diagnosing fetal craniofacial conditions.Can cleft lip be surgically corrected? Sue and Tim were referred for genetic counseling after they inquired about the risk of having a child with a cleft lip. Tim was born with a mild cleft lip that was surgically repaired. He expressed concern that his future children could be at risk for a more severe form of clefting. Sue was in her 12th week of pregnancy, and both were anxious about the pregnancy because Sue had had a difficult time conceiving. The couple stated that they would not consider terminating the pregnancy for any reason but wanted to be prepared for the possibility of having a child with a birth defect. The genetic counselor took a three-generation family history from both Sue and Tim and found that Tim was the only person to have had a cleft lip. Sues family history showed no cases of cleft lip. Tim and Sue had several misconceptions about clefting, and the genetic counselor spent time explaining how cleft lips occur and some of the known causes of this birth defect. The following list summarizes the counselors discussion with the couple. Fathers, as well as mothers, can pass on genes that cause clefting. Some clefts are caused by environmental factors, meaning that the condition didnt come from the father or the mother. One child in 33 is born with some sort of birth defect. One in 700 is born with a cleft-related birth defect. Most clefts occur in boys; however, a girl can be born with a cleft. If a person (male or female) is born with a cleft, the chances of that person having a child with a cleft, given no other obvious factor, is 7 in 100. Some clefts are related to identifiable syndromes. Of those, some are autosomal dominant. A person with an autosomal dominant gene has a 50% probability of passing the gene to an offspring. Many clefts run in families even when there does not seem to be any identifiable syndrome present. Clefting seems to be related to ethnicity, occurring most often among Asians, Latinos, and Native Americans (1 : 500); next most often among persons of European ethnicity (1 : 700); and least often among persons of African origin (1 : 1,000). A cleft condition develops during the fourth to the eighth week of pregnancy. After that critical period, nothing the mother does can cause a cleft. Sometimes a cleft develops even before the mother is aware that she is pregnant. Women who smoke are twice as likely to give birth to a child with a cleft. Women who ingest large quantities of vitamin A or low quantities of folic acid are more likely to have children with a cleft. In about 70% of cases, the fetal face is clearly visible using ultrasound. Facial disorders have been detected at the 15th gestational week of pregnancy. Ultrasound can be precise and reliable in diagnosing fetal craniofacial conditions.If the child showed a cleft lip through ultrasound analysis and the parents then started blaming each other (because Sue is a smoker and Tim was born with the defect), how would you counsel them? Sue and Tim were referred for genetic counseling after they inquired about the risk of having a child with a cleft lip. Tim was born with a mild cleft lip that was surgically repaired. He expressed concern that his future children could be at risk for a more severe form of clefting. Sue was in her 12th week of pregnancy, and both were anxious about the pregnancy because Sue had had a difficult time conceiving. The couple stated that they would not consider terminating the pregnancy for any reason but wanted to be prepared for the possibility of having a child with a birth defect. The genetic counselor took a three-generation family history from both Sue and Tim and found that Tim was the only person to have had a cleft lip. Sues family history showed no cases of cleft lip. Tim and Sue had several misconceptions about clefting, and the genetic counselor spent time explaining how cleft lips occur and some of the known causes of this birth defect. The following list summarizes the counselors discussion with the couple. Fathers, as well as mothers, can pass on genes that cause clefting. Some clefts are caused by environmental factors, meaning that the condition didnt come from the father or the mother. One child in 33 is born with some sort of birth defect. One in 700 is born with a cleft-related birth defect. Most clefts occur in boys; however, a girl can be born with a cleft. If a person (male or female) is born with a cleft, the chances of that person having a child with a cleft, given no other obvious factor, is 7 in 100. Some clefts are related to identifiable syndromes. Of those, some are autosomal dominant. A person with an autosomal dominant gene has a 50% probability of passing the gene to an offspring. Many clefts run in families even when there does not seem to be any identifiable syndrome present. Clefting seems to be related to ethnicity, occurring most often among Asians, Latinos, and Native Americans (1 : 500); next most often among persons of European ethnicity (1 : 700); and least often among persons of African origin (1 : 1,000). A cleft condition develops during the fourth to the eighth week of pregnancy. After that critical period, nothing the mother does can cause a cleft. Sometimes a cleft develops even before the mother is aware that she is pregnant. Women who smoke are twice as likely to give birth to a child with a cleft. Women who ingest large quantities of vitamin A or low quantities of folic acid are more likely to have children with a cleft. In about 70% of cases, the fetal face is clearly visible using ultrasound. Facial disorders have been detected at the 15th gestational week of pregnancy. Ultrasound can be precise and reliable in diagnosing fetal craniofacial conditions.Describe why continuous variation is common in humans and provide examples of such traits.The text outlines some of the problems Frederick William I encountered in his attempt to breed tall Potsdam Guards. a. Why were the results he obtained so different from those obtained by Mendel with short and tall pea plants? b. Why were most of the children shorter than their tall parents?What role might environment have played in causing Frederick Williams problems, especially at a time when nutrition varied greatly from town to town and from family to family?Do you think Frederick Williams experiment would have worked better if he had ordered brothersister marriages within tall families instead of just choosing the tallest individuals from throughout the country?As it turned out, one of the tallest Potsdam Guards had an unquenchable attraction to short women. During his tenure as guard, he had numerous clandestine affairs. In each case, children resulted. Subsequently, some of the childrenwho had no way of knowing that they were relatedmarried and had children of their own. Assume that two pairs of genes determine height. The genotype of the 7-foot-tall Potsdam Guard was A9A9B9B9, and the genotype of all of his 5-foot clandestine lovers was AABB. An A9 or B9 allele in the offspring each adds 6 inches to the base height of 5 feet conferred by the AABB genotype. a. What were the genotypes and phenotypes of all the F1 children? b. Diagram the cross between the F1 offspring, and give all possible genotypes and phenotypes of the F2 progenyDescribe why there is a fundamental difference between the expression of a trait that is determined by polygenes and the expression of a trait that is determined monogenetically.Sunflowers with flowers 10 cm in diameter are crossed with a plant that has 20-cm flowers. The F1 plants have flowers 15 cm in diameter. In the F2 generation, 4 flowers are 10 cm in diameter and 4 are 20 cm in diameter. Between these are 5 phenotypic classes with diameters intermediate to those at the extremes. a. Assuming that the alleles that contribute to flower diameter act additively, how many genes control flower size in this strain of sunflowers? b. How much does each additive allele contribute to flower diameter? c. What size flower makes up the largest phenotypic class?Clubfoot is a common congenital birth defect. This defect is caused by a number of genes but appears to be phenotypically distributed in a noncontinuous fashion. Geneticists use the threshold model to explain the occurrence of this defect. Explain this model. Explain predisposition to the defect in an individual who has a genotypic liability above the threshold versus an individual who has a liability below the threshold.Define genetic variance.Define environmental variance.How is heritability related to genetic and environmental variance?Why are relatives used in the calculation of heritability?If there is no genetic variation within a population for a given trait, what is the heritability for the trait in the population?Can conjoined (Siamese) twins be dizygotic twins in light of the theory that conjoined twins result from incomplete division of the embryo?Dizygotic twins: a. are as closely related as monozygotic twins b. are as closely related as non-twin siblings c. share 100% of their genetic material d. share 25% of their genetic material e. none of theseWhy are monozygotic twins who are reared apart so useful in the calculation of heritability?Monozygotic (MZ) twins have a concordance value of 44% for a specific trait, whereas dizygotic twins have a concordance value of less than 5% for the same trait. What could explain why the value for MZ twins is significantly less than 100%?If monozygotic twins show complete concordance for a trait, whether they are reared together or apart, what does this suggest about the heritability of the trait?Researchers set up an obesity study in which MZ and DZ twins who served in the armed forces were studied at induction into the military and 25 years later. Results indicated that obesity has a strong genetic component. a. What are some of the problems with this study? b. Design a better study to test whether obesity has a genetic component.What does the ob gene code for? How does it work? Is this a gene found only in animals, or do humans have it also?What is the importance of the comparison of traits between adopted and natural children in determining heritability?Height in humans is controlled by the additive action of genes and the action of environmental factors. For the purposes of this problem, assume that height is controlled by four genesA, B, C, and Dand that there are no environmental effects. Assume further that additive alleles contribute two units of height and partially additive alleles contribute one unit of height. a. Given these assumptions, can two individuals of moderate height produce offspring that are much taller and shorter than either parent? If so, how can this happen? b. Can someone of minimum height and someone of intermediate height have children taller than the parent of intermediate height? Why or why not?If diseases such as cardiovascular disease (hypertension and atherosclerosis) are familial, is this an indication that there is a genetic contribution to these traits? What would you do to confirm that genetics is involved in this condition?24QP25QPSuppose that a team of researchers analyzes the heritability of high SAT scores and assigns a heritability of 0.75 for this ability. The team also determines that a certain ethnic group has a heritability value that is 0.12 lower compared with that of other ethnic groups. The group concludes that there must be a genetic explanation for the differences in scores. Why is this an invalid conclusion?Genetics in Practice case studies are critical-thinking exercises that allow you to apply your new knowledge of human genetics to real-life problems. Case study Michelle was a 42-year-old woman who had declined counselling and amniocentesis at 16 weeks of pregnancy but was referred for genetic counseling after an abnormal ultrasound at 20 weeks of gestation. After the ultrasound, a number of findings suggested a possible chromosome abnormality in the fetus. The ultrasound showed swelling under the skin at the back of the fetuss neck; shortness of the femur, humerus, and ear length; and underdevelopment of the middle section of the fifth finger. Michelles physician performed an amniocentesis and referred her to the genetics program. Michelle and her husband did not want genetic counseling before receiving the results of the cytogenetic analysis. This was Michelles third pregnancy; she and her husband, Mike, had a 6-year-old daughter and a 3-year-old son. At their next session, the counselor informed the couple that the results revealed trisomy 21, explored their understanding of Down syndrome, and elicited their experiences with people with disabilities. She also reviewed the clinical concerns revealed by the ultrasound and associated anomalies (mild to severe intellectual disability, cardiac defects, and kidney problems). The options available to the couple were outlined. They were provided with a booklet written for parents making choices after the prenatal diagnosis of Down syndrome. After a week of careful deliberation with their family, friends, and clergy, they elected to terminate the pregnancy. Do you think that this couple had the right to terminate the pregnancy in light of the prenatal diagnosis? If not, under what circumstance would a couple have this right? What other options were available to the couple?Genetics in Practice case studies are critical-thinking exercises that allow you to apply your new knowledge of human genetics to real-life problems. Case study Michelle was a 42-year-old woman who had declined counselling and amniocentesis at 16 weeks of pregnancy but was referred for genetic counseling after an abnormal ultrasound at 20 weeks of gestation. After the ultrasound, a number of findings suggested a possible chromosome abnormality in the fetus. The ultrasound showed swelling under the skin at the back of the fetuss neck; shortness of the femur, humerus, and ear length; and underdevelopment of the middle section of the fifth finger. Michelles physician performed an amniocentesis and referred her to the genetics program. Michelle and her husband did not want genetic counseling before receiving the results of the cytogenetic analysis. This was Michelles third pregnancy; she and her husband, Mike, had a 6-year-old daughter and a 3-year-old son. At their next session, the counselor informed the couple that the results revealed trisomy 21, explored their understanding of Down syndrome, and elicited their experiences with people with disabilities. She also reviewed the clinical concerns revealed by the ultrasound and associated anomalies (mild to severe intellectual disability, cardiac defects, and kidney problems). The options available to the couple were outlined. They were provided with a booklet written for parents making choices after the prenatal diagnosis of Down syndrome. After a week of careful deliberation with their family, friends, and clergy, they elected to terminate the pregnancy. Should physicians discourage a 42-year-old woman from having children because of an increased chance of a chromosomal abnormality?Analyzing Karyotypes 1. Originally, karyotypic analysis relied only on size and centromere placement to identify chromosomes. Because many chromosomes are similar in size and centromere placement, the identification of individual chromosomes was difficult, and chromosomes were placed into eight groups, identified by the letters A to G. Today, each human chromosome can be readily identified. a. What technical advances led to this improvement in chromosome identification? b. List two ways this improvement can be implemented. c. What clinical information does a karyotype provide?Given the karyotype shown at right, is this a male or a female? Normal or abnormal? What would the phenotype of this individual be?A colleague e-mails you saying that she has identified an interesting chromosome variation at 21q13. In discussing this discovery with a friend who is not a cytogeneticist, explain how you would describe this location, defining each term in the chromosome address 21q13.What are the two most commonly used methods of prenatal diagnosis? Which technique can be performed earlier, and why is this an advantage?5QPDiscuss the following sets of terms: a. trisomy and triploidy b. aneuploidy and polyploidyWhat chromosomal abnormality can result from dispermy?Tetraploidy may result from: a. lack of cytokinesis in meiosis II b. nondisjunction in meiosis I c. lack of cytokinesis in mitosis d. nondisjunction in mitosis in the early embryo e. none of theseA cytology student believes he has identified an individual with monoploidy. The instructor views the dividing cells under the microscope and correctly dismisses the claim. Why was the claim dismissed? What types of cells were being viewed?An individual is found to have some tetraploid liver cells but diploid kidney cells. Be specific in explaining how this condition might arise.A spermatogonial cell undergoes mitosis before entering the meiotic cell cycle en route to the production of sperm. However, during mitosis the cytoplasm fails to divide, and only one daughter cell is produced. A resultant sperm eventually fertilizes a normal ovum. What is the chromosomal complement of the embryo?A teratogen is an agent that produces nongenetic abnormalities during embryonic or fetal development. Suppose a teratogen is present at conception. As a result, during the first mitotic division the centromeres fail to divide. The teratogen then loses its potency and has no further effect on the embryo. What is the chromosomal complement of this embryo?As a physician, you deliver a baby with protruding heels and clenched fists with the second and fifth fingers over-lapping the third and fourth fingers. a. What genetic disorder do you suspect the baby has? b. How do you confirm your suspicion?Variations in Chromosome NumberAneuploidy Describe the process of nondisjunction and explain when it takes place during cell division.A woman gives birth to monozygotic twins. One boy has a normal genotype (46, XY), but the other boy has trisomy 13 (47, +13). What eventsand in what sequenceled to this situation?Assume that a meiotic-nondisjunction event causes trisomy 8 in a newborn. If two of the three copies of chromosome 8 are absolutely identical, at what point during meiosis did the nondisjunction event take place?17QPWhat is the genetic basis and phenotype for each of the following disorders (use proper genetic notation)? a. Edwards syndrome b. Patau syndrome c. Klinefelter syndrome d. Down syndromeThe majority of nondisjunction events leading to Down syndrome are maternal in origin. Based on the duration of meiosis in females, speculate on the possible reasons for females contributing aneuploid gametes more frequently than males do.20QPIf all the nondisjunction events leading to Turner syndrome were paternal in origin, what trisomic condition might be expected to occur at least as frequently?Identify the type of chromosomal aberration described in each of the following cases: a. loss of a chromosome segment b. extra copies of a chromosome segment c. reversal in the order of a chromosome segment d. movement of a chromosome segment to another, nonhomologous chromosomeDescribe the chromosomal alterations and phenotype of cri du chat syndrome and Prader-Willi syndrome.A geneticist discovers that a girl with Down syndrome has a Robertsonian translocation involving chromosomes 14 and 21. If she has an older brother who is phenotypically normal, what are the chances that he is a translocation carrier?Albinism is caused by an autosomal recessive allele of a single gene. An albino child is born to phenotypically normal parents. However, the paternal grandfather is albino. Exhaustive analysis suggests that neither the mother nor her ancestors carry the allele for albinism. Suggest a mechanism to explain this situation.Fragile-X syndrome causes the most common form of inherited intellectual disability. What is the chromosomal abnormality associated with this disorder? What is the phenotype of this disorder?1EG2EGAs outlined in this chapter, sex can be defined at several levels: chromosomal, gonadal, and phenotypic. To this we can add psychological sex, the sex one believes themselves to be. Determining someones sex is a complex issue that is often difficult to resolve, as the case of Bruce Reimer (see Section 7.1) illustrates. In spite of the complexity surrounding this issue, the International Olympic Committee (IOC) and the International Association of Athletics Federations (IAFF) still use sex testing on female athletes to determine whether they can compete in athletic events as females. This has led to serious personal, social, and legal issues, and the practice has been widely condemned and widely defended. Lets examine two such cases here. An Indian athlete, Santhi Soundarajan, finished second in the 800-meter run at the Asian Games in Doha, Qatar, in 2006. After the race, she was asked to take a sex test. According to press reports, the tests showed that she appeared to have abnormal chromosomes. An official stated that she had more Y chromosomes than allowed. As a result, she was stripped of her medal, banned from further competition by the Indian Olympic Association, and shunned by her local community. Before the race in Doha, Santhi had competed in 8 international competitions and won 12 medals. Sometime after this incident, she attempted suicide. She now runs a training school for athletes in Tamil Nadu, India. Although the number and types of tests done on Santhi have not been revealed, such tests usually involve examination of the external genitals, a chromosome analysis, and measurement of hormone levels. Suppose you were on the committee deciding whether Santhi could compete as a female. Consider each of the following hypothetical tests one at a time and base your conclusions only on the results of that test. The results of a physical examination show she has female genitals. On this basis, would you allow her to keep her medal and compete as a female in future races? Suppose the results of a chromosomal analysis shows that she has an XY chromosome set and is chromosomally male. Would you allow her to keep her medal and compete as a female? Lastly, suppose a test for hormone levels shows that she has levels of the male sex hormone testosterone that are higher than average for females but at least 10 times lower than the average for males. Would you allow her to keep her medal and compete in future races as a female? Now, put the results of all three tests together, and consider them as a whole. What are your conclusions? Now, lets consider the case of a South African runner, Caster Semenya, who won the 800-meter run at the World Championships held in Berlin, Germany, in 2009. After the race, she was asked to undergo sex testing. The IAAF stated that the tests were requested to ascertain whether she had a rare medical condition that gave her an unfair physical advantage. The nature of the tests and their results were not released, but press reports indicate that she did not have ovaries or a uterus, and had testosterone levels intermediate between the averages for males and females. In the end, the IAAF agreed to keep the results of her tests confidential, and Caster was allowed to keep her medal and return to international competition in 2010. In both cases, what the IAAF considers the threshold for determining who can compete as a female has not been stated. Based on what is known about the test results in this case and the hypothetical tests in the first case, do you think the outcome in each case was fair?As outlined in this chapter, sex can be defined at several levels: chromosomal, gonadal, and phenotypic. To this we can add psychological sex, the sex one believes themselves to be. Determining someones sex is a complex issue that is often difficult to resolve, as the case of Bruce Reimer (see Section 7.1) illustrates. In spite of the complexity surrounding this issue, the International Olympic Committee (IOC) and the International Association of Athletics Federations (IAFF) still use sex testing on female athletes to determine whether they can compete in athletic events as females. This has led to serious personal, social, and legal issues, and the practice has been widely condemned and widely defended. Lets examine two such cases here. An Indian athlete, Santhi Soundarajan, finished second in the 800-meter run at the Asian Games in Doha, Qatar, in 2006. After the race, she was asked to take a sex test. According to press reports, the tests showed that she appeared to have abnormal chromosomes. An official stated that she had more Y chromosomes than allowed. As a result, she was stripped of her medal, banned from further competition by the Indian Olympic Association, and shunned by her local community. Before the race in Doha, Santhi had competed in 8 international competitions and won 12 medals. Sometime after this incident, she attempted suicide. She now runs a training school for athletes in Tamil Nadu, India. Although the number and types of tests done on Santhi have not been revealed, such tests usually involve examination of the external genitals, a chromosome analysis, and measurement of hormone levels. Suppose you were on the committee deciding whether Santhi could compete as a female. Consider each of the following hypothetical tests one at a time and base your conclusions only on the results of that test. The results of a physical examination show she has female genitals. On this basis, would you allow her to keep her medal and compete as a female in future races? Suppose the results of a chromosomal analysis shows that she has an XY chromosome set and is chromosomally male. Would you allow her to keep her medal and compete as a female? Lastly, suppose a test for hormone levels shows that she has levels of the male sex hormone testosterone that are higher than average for females but at least 10 times lower than the average for males. Would you allow her to keep her medal and compete in future races as a female? Now, put the results of all three tests together, and consider them as a whole. What are your conclusions? Now, lets consider the case of a South African runner, Caster Semenya, who won the 800-meter run at the World Championships held in Berlin, Germany, in 2009. After the race, she was asked to undergo sex testing. The IAAF stated that the tests were requested to ascertain whether she had a rare medical condition that gave her an unfair physical advantage. The nature of the tests and their results were not released, but press reports indicate that she did not have ovaries or a uterus, and had testosterone levels intermediate between the averages for males and females. In the end, the IAAF agreed to keep the results of her tests confidential, and Caster was allowed to keep her medal and return to international competition in 2010. In both cases, what the IAAF considers the threshold for determining who can compete as a female has not been stated. Would you recommend that testing of female athletes be continued to ensure that males do not compete as females? Or should all such testing be banned?1QPThe Human Reproductive System Discuss and compare the products of meiosis in human females and males. How many functional gametes are produced from the daughter cells in each sex?3QPA Survey of Human Development from Fertilization to Birth 4. The gestation of a fetus occurs over 9 months and is divided into three trimesters. Describe the major events that occur in each trimester. Is there a point at which the fetus becomes more human?5QP6QP7QPHow Is Sex Determined? The absence of a Y chromosome in an early embryo causes the: a. embryonic testis to become an ovary b. Wolffian duct system to develop c. Mllerian duct system to degenerate d. indifferent gonad to become an ovary e. indifferent gonad to become a testis9QPMutations Can Uncouple Chromosomal Sex from Phenotypic Sex Give an example of a situation in which genetic sex, gonadal sex, and phenotypic sex do not coincide. Explain why they do not coincide.11QPMutations Can Uncouple chromosomal Sex from Phenotypic Sex Discuss whether the following individuals (1) have male or female gonads, (2) are phenotypically male or female (discuss Wolffian/Mllerian ducts and external genitalia), and (3) are sterile or fertile. a. XY, homozygous for a recessive mutation in the testosterone biosynthetic pathway, producing no testosterone b. XX, heterozygous for a dominant mutation in the testosterone biosynthetic pathway, which causes continuous production of testosterone c. XY, heterozygous for a recessive mutation in the MIH gene d. XY, homozygous fora recessive mutation in the SRY gene that abolishes function13QPSex-Influenced and Sex-Limited Traits What method of sex testing did the International Olympic Committee previously use? What method did it use subsequently? Does either of these methods conclusively test for femaleness? Explain.15QP16QPEqualizing the Expression of X Chromosome Genes in Males and Females How many Barr bodies would the following individuals have? a. normal male b. normal female c. Klinefelter male d. Turner femaleEqualizing the Expression of X Chromosome Genes in Males and Females Males have only one X chromosome and therefore only one copy of all genes on the X chromosome. Each gene is directly expressed, thus providing the basis of hemizygosity in males. Females have two X chromosomes, but one is always inactivated. Therefore, females, like males, have only one functional copy of all the genes on the X chromosome. Again, each gene must be directly expressed. Why, then, are females not considered hemizygous, and why are they not afflicted with sex-linked recessive diseases as often as males are?Equalizing the Expression of X Chromosome Genes in Males and Females Individuals with an XXY genotype are sterile males. If one X is inactivated early in embryogenesis, the genotype of the individual effectively becomes XY. Why will this individual not develop as a normal male?Two genes associated with breast cancer, BRCA1 and BRCA2, were discovered in 1994 and 1995, respectively, and shortly thereafter, were patented by Myriad Genetics, a company based in Utah. Under the patents, testing for mutations in these genes could only be performed by Myriad, at costs from 300 to 3,000. Myriad also patented the process of analyzing the results of such tests, preventing anyone who obtains the sequence of their BRCA genes by other means (which itself would probably be patent infringement) from interpreting the information. The idea that genes can be patented has been a contentious issue from the beginning. Patents are not granted for products of nature, meaning that genes inside the body are not patentable, but biotech companies successfully argued that by removing a gene from the human body, purifying it, and then obtaining its DNA sequence, they created something not found in nature, and which is therefore a patentable invention. The U.S. Patent Office found the argument persuasive, but opponents argue that genes are parts of our bodies and can be identified but not invented. Biotech companies argue that without the protection offered by patents, they would have no incentive for research and development of diagnostic tests. In Europe, patents for BRCA1 and BRCA2 were revoked in 2004 because they did not meet the standards for a patent. After more than a decade of legal disputes, the patents were partially restored in 2008 on a very restricted basis. In the United States, a lawsuit, focused on the patents for the BRCA genes, was filed in May 2009. The suit challenges the basic idea that genes are patentable. In November 2009, the judge ruled that the lawsuit can proceed, and the case is moving forward. In March 2010, a federal court invalidated Myriad Genetics patent on these genes. In August 2011, the U.S. Court of Appeals reversed the lower courts decision and ruled that gene sequences isolated from cells are not a product of nature and are therefore patentable. The case went to the U.S. Supreme Court, which ordered the appeals court to reconsider the case. The Federal Appeals Court did not change its decision, and the case once again, went to the U.S. Supreme Court. A unanimous decision in June 2013 invalidated Myriads patents on the basis that isolating a gene from nature does not make it patentable. This is a landmark decision on gene patenting with widespread ramifications for the biotechnoloogy industry. Will this decision reduce the incentives for companies to invest in new diagnostic tests that would be used by cancer victims or those with serious genetic disorders?2GRWhat are Bruces options at this point? Bruce and his parents moved to a semi-tropical region of the United States when he was about 3 years old. He loved to be outside year-round and swim, surf, snorkel, and play baseball. Bruce was fair-skinned, and in his childhood years, was sunburned quite often. In his teen years, he began using sunscreens, and although he never tanned very much, he did not have the painful sunburns of his younger years. After graduation from the local community college, Bruce wanted an outdoor job and was hired at a dive shop. He took people out to one of the local reefs to snorkel and scuba dive. He didnt give a second thought to sun exposure because he used sunscreen. His employer did not provide health insurance, so Bruce did not go for annual checkups, and tried to stay in good health. In his late 20s, Bruce was injured trying to keep a tourist from getting caught between the dive boat and the dock. He went to an internist, who treated his injury and told Bruce he was going to give him a complete physical exam. During the exam, the internist noticed a discolored patch of skin on Bruces back. She told him that she suspected Bruce had skin cancer and referred him to a dermatologist, who biopsied the patch. At a follow-up visit, Bruce was told that he had melanoma, a deadly form of skin cancer. Further testing revealed that the melanoma had spread to his liver and his lungs. The dermatologist explained that treatment options at this stage are limited. The drugs available for chemotherapy have only temporary effects, and surgery is not effective for melanoma at this stage. The dermatologist recommended that Bruce consider entering a clinical trial that was testing a DNA vaccine for melanoma treatment. These vaccines deliver DNA encoding a gene expressed by the cancer cells to the immune system. This primes the immune system to respond by producing large quantities of antibodies that destroy melanoma cells wherever they occur in the body. A clinical trial using one such DNA vaccine was being conducted at a nearby medical center, and Bruce decided to participate. At the study clinic, Bruce learned that he would be in a Phase Ill trial, comparing the DNA vaccine against the standard treatment, which is chemotherapy, and that he would be randomly assigned to receive either the DNA vaccine or the chemotherapy. He was disappointed to learn this. He thought he would be receiving the DNA vaccine.Should he reconsider and try chemotherapy instead? Bruce and his parents moved to a semi-tropical region of the United States when he was about 3 years old. He loved to be outside year-round and swim, surf, snorkel, and play baseball. Bruce was fair-skinned, and in his childhood years, was sunburned quite often. In his teen years, he began using sunscreens, and although he never tanned very much, he did not have the painful sunburns of his younger years. After graduation from the local community college, Bruce wanted an outdoor job and was hired at a dive shop. He took people out to one of the local reefs to snorkel and scuba dive. He didnt give a second thought to sun exposure because he used sunscreen. His employer did not provide health insurance, so Bruce did not go for annual checkups, and tried to stay in good health. In his late 20s, Bruce was injured trying to keep a tourist from getting caught between the dive boat and the dock. He went to an internist, who treated his injury and told Bruce he was going to give him a complete physical exam. During the exam, the internist noticed a discolored patch of skin on Bruces back. She told him that she suspected Bruce had skin cancer and referred him to a dermatologist, who biopsied the patch. At a follow-up visit, Bruce was told that he had melanoma, a deadly form of skin cancer. Further testing revealed that the melanoma had spread to his liver and his lungs. The dermatologist explained that treatment options at this stage are limited. The drugs available for chemotherapy have only temporary effects, and surgery is not effective for melanoma at this stage. The dermatologist recommended that Bruce consider entering a clinical trial that was testing a DNA vaccine for melanoma treatment. These vaccines deliver DNA encoding a gene expressed by the cancer cells to the immune system. This primes the immune system to respond by producing large quantities of antibodies that destroy melanoma cells wherever they occur in the body. A clinical trial using one such DNA vaccine was being conducted at a nearby medical center, and Bruce decided to participate. At the study clinic, Bruce learned that he would be in a Phase Ill trial, comparing the DNA vaccine against the standard treatment, which is chemotherapy, and that he would be randomly assigned to receive either the DNA vaccine or the chemotherapy. He was disappointed to learn this. He thought he would be receiving the DNA vaccine.Should he go ahead and enroll on the chance that he would receive the DNA vaccine and that it would be more effective than chemotherapy? Bruce and his parents moved to a semi-tropical region of the United States when he was about 3 years old. He loved to be outside year-round and swim, surf, snorkel, and play baseball. Bruce was fair-skinned, and in his childhood years, was sunburned quite often. In his teen years, he began using sunscreens, and although he never tanned very much, he did not have the painful sunburns of his younger years. After graduation from the local community college, Bruce wanted an outdoor job and was hired at a dive shop. He took people out to one of the local reefs to snorkel and scuba dive. He didnt give a second thought to sun exposure because he used sunscreen. His employer did not provide health insurance, so Bruce did not go for annual checkups, and tried to stay in good health. In his late 20s, Bruce was injured trying to keep a tourist from getting caught between the dive boat and the dock. He went to an internist, who treated his injury and told Bruce he was going to give him a complete physical exam. During the exam, the internist noticed a discolored patch of skin on Bruces back. She told him that she suspected Bruce had skin cancer and referred him to a dermatologist, who biopsied the patch. At a follow-up visit, Bruce was told that he had melanoma, a deadly form of skin cancer. Further testing revealed that the melanoma had spread to his liver and his lungs. The dermatologist explained that treatment options at this stage are limited. The drugs available for chemotherapy have only temporary effects, and surgery is not effective for melanoma at this stage. The dermatologist recommended that Bruce consider entering a clinical trial that was testing a DNA vaccine for melanoma treatment. These vaccines deliver DNA encoding a gene expressed by the cancer cells to the immune system. This primes the immune system to respond by producing large quantities of antibodies that destroy melanoma cells wherever they occur in the body. A clinical trial using one such DNA vaccine was being conducted at a nearby medical center, and Bruce decided to participate. At the study clinic, Bruce learned that he would be in a Phase Ill trial, comparing the DNA vaccine against the standard treatment, which is chemotherapy, and that he would be randomly assigned to receive either the DNA vaccine or the chemotherapy. He was disappointed to learn this. He thought he would be receiving the DNA vaccine.Until 1944, which cellular component was thought to carry genetic information? a. carbohydrate b. nucleic acid c. protein d. chromatin e. lipidWhy do you think nucleic acids were originally not considered to be carriers of genetic information?3QPIn the experiments of Aery, MacLeod, and McCarty, what was the purpose of treating the transforming extract with enzymes?Read the following experiment and interpret the results to form your conclusion. Experimental data: S bacteria were heat killed and cell extracts were isolated. The extracts contained cellular components, including lipids, proteins, DNA, and RNA. The extracts were mixed with live R bacteria and then injected together into mice along with various enzymes (proteases, RNAses, and DNAses). Proteases degrade proteins, RNAses degrade RNA, and DNAses degrade DNA. Based on these results, what is the transforming principle?Recently, scientists discovered that a rare disorder called polkadotism is caused by a bacterial strain, polkadotiae. Mice injected with this strain (P) develop polka dots on their skin. Heat-killed P bacteria and live D bacteria, a nonvirulent strain, do not produce polka dots when injected separately into mice. However, when a mixture of heat-killed P cells and live D cells were injected together, the mice developed polka dots. What process explains this result? Describe what is happening in the mouse to cause this outcome.List the pyrimidine bases, the purine bases, and the base-pairing rules for DNA.In analyzing the base composition of a DNA sample, a student loses the information on pyrimidine content. The purine content is A = 27% and G = 23%. Using Chargaffs rule, reconstruct the missing data and list the base composition of the DNA sample.The basic building blocks of nucleic acids are: a. phosphate groups b. nucleotides c. ribose sugars d. amino acids e. purine basesAdenine is a: a. nucleoside b. purine c. pyrimidine d. nucleotide e. basePolynucleotide chains have a 5 and a 3 end. Which groups are found at each of these ends? a. 5 sugars, 3 phosphates b. 3 OH, 5 phosphates c. 3 base, 5 phosphates d. 5 base, 3 OH e. 5 phosphates, 3 basesDNA contains many hydrogen bonds. Are hydrogen bonds stronger or weaker than covalent bonds? What are the consequences of this difference in strength?13QPState the properties of the WatsonCrick model of DNA in the following categories: a. number of polynucleotide chains b. polarity (running in same direction or opposite directions) c. bases on interior or exterior of molecule d. sugar/phosphate on interior or exterior of molecule e. which bases pair with which f. right- or left-handed helixUsing Figures 8.7 and 8.9 as a guide, draw a dinucleotide composed of C and A. Next to this, draw the complementary dinucleotide in an antiparallel fashion. Connect the dinucleotides with the appropriate hydrogen bonds. FIGURE 8.9 The two polynucleotide chains in DNA run in opposite directions. The left strand runs 5 to 3, and the right strand runs 3 to 5. The base sequences in each strand are complementary. An A in one strand pairs with a T in the other strand, and a C in one strand is paired with a G in the opposite strand. FIGURE 8.7 Nucleotides can be joined together to form chains caled polynucleotides. Polynucleotides are polar molecules with a 5 end (at the phosphate group) and a 3 end (at the sugar group). An RNA polynucleotide is shown at the left, and a DNA polynucleotide is shown at the right.A beginning genetics student is attempting to complete an assignment to draw a base pair from a DNA molecule. The drawing is incomplete, and the student does not know how to finish. He asks for your advice. The assignment sheet shows that the drawing is to contain three hydrogen bonds, a purine, and a pyrimidine. From your knowledge of the pairing rules and the number of hydrogen bonds in A/T and G/C base pairs, what base pair do you help the student draw?Chemical analysis shows that a nucleic acid sample contains A, U, C, and G. Is this DNA or RNA? Why?18QPRNA is ribonucleic acid, and DNA is deoxyribonucleic acid. What exactly is deoxygenated about DNA?What is the function of DNA polymerase? a. It degrades DNA in cells. b. It adds RNA nucleotides to a new strand. c. It coils DNA around histones to form chromosomes. d. It adds DNA nucleotides to a replicating strand. e. None of these.Which of the following statements is not true about DNA replication? a. It occurs during the M phase of the cell cycle. b. It makes a sister chromatid. c. It denatures DNA strands. d. It occurs semiconservatively. e. It follows base-pairing rules.Make the complementary strand for the following DNA template and label both strands as 5 to 3 or 3 to 5 (P = phosphate in the diagram). Draw an arrow showing the direction of synthesis of the new strand. How many hydrogen bonds are in this double strand of DNA? template: PAGGCTCGOH new strand:How does DNA replication occur in a precise manner to ensure that identical genetic information is put into the new chromatid? See Figures 8.12 and 8.13. FIGURE 8.12 In DNA replication, the two polynucleotide strands uncoil, and each is a template for synthesizing a new strand. A replicated DNA molecule contains one new strand and one old strand. This mechanism is called semiconservative replication. FIGURE 8.13 A close-up look at the process of DNA replication. (a) As the strands uncoil, bases are added to the newly synthesized strand by complementary base pairing with bases in the template strand. The new bases are linked together by DNA polymerase. (b) DNA synthesis can proceed only in the 5 3 direction; newly synthesized DNA on one template strand is made in short segments and linked together by the enzyme DNA ligase.Nucleosomes are complexes of: a. RNA and DNA b. RNA and histone c. histones and DNA d. DNA, RNA, and protein e. amino acids and DNADiscuss the levels of chromosomal organization with reference to the following terms: a. nucleotide b. DNA double helix c. histones d. nucleosomes e. chromatinAntibiotics and Protein Synthesis Antibiotics are molecules produced by microorganisms as defense mechanisms. The most effective antibiotics work by interfering with essential biochemical or reproductive processes. Many antibiotics block or disrupt one or more stages in protein synthesis. Some of these are mentioned here. Tetracyclines are a family of chemically related compounds used to treat several types of bacterial infections. Tetracyclines interfere with the initiation of translation. The tetracycline molecule attaches to the small ribosomal subunit and prevents binding of the tRNA anticodon during initiation. Both eukaryotic and prokaryotic ribosomes are sensitive to the action of tetracycline, but this antibiotic cannot pass through the plasma membrane of eukaryotic cells. Because tetracycline can enter bacterial cells to inhibit protein synthesis, it will stop bacterial growth, helping the immune system fight the infection. Streptomycin is used in hospitals to treat serious bacterial infections. It binds to the small ribosomal subunit but does not prevent initiation or elongation; however, it does affect the efficiency of protein synthesis. Binding of streptomycin changes the way mRNA codons interact with the tRNA. As a result, incorrect amino acids are incorporated into the growing polypeptide chain, producing nonfunctional proteins. In addition, streptomycin causes the ribosome to randomly fall off the mRNA, preventing the synthesis of complete proteins. Puromycin is not used clinically but has played an important role in studying the mechanism of protein synthesis in the research laboratory. The puromycin molecule is the same size and shape as a tRNA/amino acid complex. When puromycin enters the ribosome, it can be incorporated into a growing polypeptide chain, stopping further synthesis because no peptide bond can be formed between puromycin and an amino acid, causing the shortened polypeptide to fall off the ribosome. Chloramphenicol was one of the first broadspectrum antibiotics introduced. Eukaryotic cells are resistant to its actions, and it was widely used to treat bacterial infections. However, its use is limited to external applications and serious infections. Chloramphenicol destroys cells in the bone marrow, the source of all blood cells. In bacteria, this antibiotic binds to the large ribosomal subunit and inhibits the formation of peptide bonds. Another antibiotic, erythromycin, also binds to the large ribosomal subunit and inhibits the movement of ribosomes along the mRNA. Almost every step of protein synthesis can be inhibited by one antibiotic or another. Work on designing new synthetic antibiotics to fight infections is based on our knowledge of how the nucleotide sequence of mRNA is converted into the amino acid sequence of a protein. Questions Why are antibiotics ineffective in treating the common cold and other virus infections?Antibiotics and Protein Synthesis Antibiotics are molecules produced by microorganisms as defense mechanisms. The most effective antibiotics work by interfering with essential biochemical or reproductive processes. Many antibiotics block or disrupt one or more stages in protein synthesis. Some of these are mentioned here. Tetracyclines are a family of chemically related compounds used to treat several types of bacterial infections. Tetracyclines interfere with the initiation of translation. The tetracycline molecule attaches to the small ribosomal subunit and prevents binding of the tRNA anticodon during initiation. Both eukaryotic and prokaryotic ribosomes are sensitive to the action of tetracycline, but this antibiotic cannot pass through the plasma membrane of eukaryotic cells. Because tetracycline can enter bacterial cells to inhibit protein synthesis, it will stop bacterial growth, helping the immune system fight the infection. Streptomycin is used in hospitals to treat serious bacterial infections. It binds to the small ribosomal subunit but does not prevent initiation or elongation; however, it does affect the efficiency of protein synthesis. Binding of streptomycin changes the way mRNA codons interact with the tRNA. As a result, incorrect amino acids are incorporated into the growing polypeptide chain, producing nonfunctional proteins. In addition, streptomycin causes the ribosome to randomly fall off the mRNA, preventing the synthesis of complete proteins. Puromycin is not used clinically but has played an important role in studying the mechanism of protein synthesis in the research laboratory. The puromycin molecule is the same size and shape as a tRNA/amino acid complex. When puromycin enters the ribosome, it can be incorporated into a growing polypeptide chain, stopping further synthesis because no peptide bond can be formed between puromycin and an amino acid, causing the shortened polypeptide to fall off the ribosome. Chloramphenicol was one of the first broadspectrum antibiotics introduced. Eukaryotic cells are resistant to its actions, and it was widely used to treat bacterial infections. However, its use is limited to external applications and serious infections. Chloramphenicol destroys cells in the bone marrow, the source of all blood cells. In bacteria, this antibiotic binds to the large ribosomal subunit and inhibits the formation of peptide bonds. Another antibiotic, erythromycin, also binds to the large ribosomal subunit and inhibits the movement of ribosomes along the mRNA. Almost every step of protein synthesis can be inhibited by one antibiotic or another. Work on designing new synthetic antibiotics to fight infections is based on our knowledge of how the nucleotide sequence of mRNA is converted into the amino acid sequence of a protein. Questions Why is targeting protein synthesis an effective strategy for preventing infection?There have been recurring cases of mad-cow disease in the United Kingdom since the mid-1990s. Mad-cow disease is caused by a prion, an infectious particle that consists only of protein. In 1986, the media began reporting that cows all over England were dying from a mysterious disease. Initially, there was little interest in determining whether humans could be affected. For 10 years, the British government maintained that this unusual disease could not be transmitted to humans. However, in March 1996, the government did an about-face and announced that bovine spongiform encephalopathy (BSE), commonly known as mad-cow disease, can be transmitted to humans, where it is known as variant Creutzfeldt-Jakob disease (VCJD). As in cows, this disease eats away at the nervous system, destroying the brain and essentially turning it into a spongelike structure filled with holes. Victims experience dementia; confusion; loss of speech, sight, and hearing; convulsions; coma; and finally death. Prion diseases are always fatal, and there is no treatment. Precautionary measures taken in Britain to prevent this disease in humans may have begun too late. Many of the victims contracted it over a decade earlier, when the BSE epidemic began, and the incubation period is long (VCJD has an incubation period of 10 to 40 years). A recent study concluded that 1 in 2,000 people in Great Britain carry the abnormally folded protein that causes VCJD. In spite of these numbers, the death rate from VCJD remains low. It is not clear whether this means that the incubation period for the disease is much longer than previously thought, or whether they may never develop the disease. How can a prion replicate itself without genetic material?There have been recurring cases of mad-cow disease in the United Kingdom since the mid-1990s. Mad-cow disease is caused by a prion, an infectious particle that consists only of protein. In 1986, the media began reporting that cows all over England were dying from a mysterious disease. Initially, there was little interest in determining whether humans could be affected. For 10 years, the British government maintained that this unusual disease could not be transmitted to humans. However, in March 1996, the government did an about-face and announced that bovine spongiform encephalopathy (BSE), commonly known as mad-cow disease, can be transmitted to humans, where it is known as variant Creutzfeldt-Jakob disease (vCJD). As in cows, this disease eats away at the nervous system, destroying the brain and essentially turning it into a spongelike structure filled with holes. Victims experience dementia; confusion; loss of speech, sight, and hearing; convulsions; coma; and finally death. Prion diseases are always fatal, and there is no treatment. Precautionary measures taken in Britain to prevent this disease in humans may have begun too late. Many of the victims contracted it over a decade earlier, when the BSE epidemic began, and the incubation period is long (vCJD has an incubation period of 10 to 40 years). A recent study concluded that 1 in 2,000 people in Great Britain carry the abnormally folded protein that causes vCJD. In spite of these numbers, the death rate from vCJD remains low. It is not clear whether this means that the incubation period for the disease is much longer than previously thought, or whether they may never develop the disease. What measures have been taken to stop BSE?There have been recurring cases of mad-cow disease in the United Kingdom since the mid-1990s. Mad-cow disease is caused by a prion, an infectious particle that consists only of protein. In 1986, the media began reporting that cows all over England were dying from a mysterious disease. Initially, there was little interest in determining whether humans could be affected. For 10 years, the British government maintained that this unusual disease could not be transmitted to humans. However, in March 1996, the government did an about-face and announced that bovine spongiform encephalopathy (BSE), commonly known as mad-cow disease, can be transmitted to humans, where it is known as variant Creutzfeldt-Jakob disease (vCJD). As in cows, this disease eats away at the nervous system, destroying the brain and essentially turning it into a spongelike structure filled with holes. Victims experience dementia; confusion; loss of speech, sight, and hearing; convulsions; coma; and finally death. Prion diseases are always fatal, and there is no treatment. Precautionary measures taken in Britain to prevent this disease in humans may have begun too late. Many of the victims contracted it over a decade earlier, when the BSE epidemic began, and the incubation period is long (vCJD has an incubation period of 10 to 40 years). A recent study concluded that 1 in 2,000 people in Great Britain carry the abnormally folded protein that causes vCJD. In spite of these numbers, the death rate from vCJD remains low. It is not clear whether this means that the incubation period for the disease is much longer than previously thought, or whether they may never develop the disease. If you were traveling in Europe, would you eat beef? Give sound reasons why or why not.The Link Between Genes and proteins The genetic material has to store information and be able to express it. What is the relationship among DNA, RNA, proteins, and phenotype?Define replication, transcription, and translation. In what part of the cell does each process occur?If the genetic code used 4 bases at a time, how many amino acids could be encoded?If the genetic code uses triplets, how many different amino acids can be coded by a repeating RNA polymer composed of UA and UC (UAUCUAUCUAUC ...)? a. one b. two c. three d. four e. fiveWhat is the start codon? What are the stop codons? Do any of them code for amino acids?Is an entire chromosome made into an mRNA during transcription?The promoter and terminator regions of genes are important in: a. coding for amino acids b. gene regulation c. structural support for the gene d. intron removal e. anticodon recognitionThe following segment of DNA codes for a protein. The uppercase letters represent exons. The lowercase letters represent introns. The lower strand is the template strand. Draw the primary transcript and the mRNA resulting from this DNA.What are the three modifications made to pre-mRNA molecules before they become mature mRNAs, are transported from the nucleus to the cytoplasm, and become ready to be used in protein synthesis? What is the function of each modification?The pre-mRNA transcript and protein made by several mutant genes were examined. The results are given below. Determine where in the gene a likely mutation lies: the promoter region, exon, intron, cap on mRNA, or ribosome binding site. a. normal-length transcript, normal-length nonfunctional protein b. normal-length transcript, no protein made c. normal-length transcript, normal-length mRNA, short nonfunctional protein d. normal-length transcript, longer mRNA, shorter nonfunctional protein e. transcript never madeBriefly describe the function of the following in protein synthesis. a. rRNA b. tRNA c. mRNA12QPDetermine the percent of the following gene that will code for the protein product. Gene length is measured in kilobases (kb) of DNA. Each kilobase is 1,000 bases long.How many kilobases of the DNA strand below will code for the protein product?15QPGiven the following tRNA anticodon sequence, derive the mRNA and the DNA template strand. Also, write out the amino acid sequence of the protein encoded by this message. tRNA: UAC UCU CGA GGC mRNA: protein: How many hydrogen bonds would be present in the DNA segment?Given the following mRNA, write the double-stranded DNA segment that served as the template. Indicate both the 5 and the 3 ends of both DNA strands. Also write out the tRNA anticodons and the amino acid sequence of the protein encoded by the mRNA message. DNA: mRNA: 5-CCGCAUGUUCAGUGGGCGUAAACACUGA-3 protein: tRNA:The following is a portion of a protein: met-trp-tyr-arg-gly-pro-thr-Various mutant forms of this protein have been recovered. Using the normal and mutant sequences, determine the DNA and mRNA sequences that code for this portion of the protein, and explain each of the mutations. a. met-trp- b. met-cys-ile-val-val-leu-gln- c. met-trp-tyr-arg-ser-pro-thr- d. met-trp-tyr-arg-gly-ala-val-ile-ser-pro-thr-Below is the structure of glycine. Draw a tripeptide composed exclusively of glycine. Label the N-terminus and C-terminus. Draw a box around the peptide bonds.Indicate in which category, transcription or translation, each of the following functions belongs: RNA poly-merase, ribosomes, nucleotides, tRNA, pre-mRNA, DNA, anticodon, amino acids.21QPPolypeptide folding is often mediated by other proteins called chaperones. Describe how a mutant chaperone protein might be responsible for a genetic disorder involving an enzyme.Do mutations in DNA alter proteins all the time?a. Can a mutation change a proteins tertiary structure without changing its primary structure? b. Can a mutation change a proteins primary structure without affecting its secondary structure?1GR2GR1EG2EGA couple was referred for genetic counseling because they wanted to know the chances of having a child with dwarfism. Both the man and the woman had achondroplasia (MIM 100800), the most common form of short-limbed dwarfism. The couple knew that this condition is inherited as an autosomal dominant trait, but they were unsure what kind of physical manifestations a child would have if it inherited both mutant alleles. They were each heterozygous for the FGFR3 (MIM 134934) allele that causes achondroplasia. Normally, the protein encoded by this gene interacts with growth factors outside the cell and receives signals that control growth and development. In achrodroplasia, a mutation alters the activity of the receptor, resulting in a characteristic form of dwarfism. Because both the normal and mutant forms of the FGFR3 protein act before birth, no treatment for achrondroplasia is available. The parents each carry one normal allele and one mutant allele of FGRF3, and they wanted information on their chances of having a homozygous child. The counsellor briefly reviewed the phenotypic features of individuals with achondroplasia. These include facial features (large head with prominent forehead; small, flat nasal bridge; and prominent jaw), very short stature, and shortening of the arms and legs. Physical examination and skeletal X-ray films are used to diagnose this condition. Final adult height is approximately 4 feet. Because achondroplasia is an autosomal dominant condition, a heterozygote has a 1-in-2, or 50%, chance of passing this trait to his or her offspring. However, about 75% of those with achondroplasia have parents of average size who do not carry the mutant allele. In these cases, achondroplasia is due to a new mutation. In the couple being counseled, each individual is heterozygous, and they are at risk for having a homozygous child with two copies of the mutated gene. Infants with homozygous achondroplasia are either stillborn or die shortly after birth. The counselor recommended prenatal diagnosis via ultrasounds at various stages of development. In addition, a DNA test is available to detect the homozygous condition prenatally. What is the chance that this couple will have a child with two copies of the dominant mutant gene? What is the chance that the child will have normal height?A couple was referred for genetic counseling because they wanted to know the chances of having a child with dwarfism. Both the man and the woman had achondroplasia (MIM 100800), the most common form of short-limbed dwarfism. The couple knew that this condition is inherited as an autosomal dominant trait, but they were unsure what kind of physical manifestations a child would have if it inherited both mutant alleles. They were each heterozygous for the FGFR3 (MIM 134934) allele that causes achondroplasia. Normally, the protein encoded by this gene interacts with growth factors outside the cell and receives signals that control growth and development. In achrodroplasia, a mutation alters the activity of the receptor, resulting in a characteristic form of dwarfism. Because both the normal and mutant forms of the FGFR3 protein act before birth, no treatment for achrondroplasia is available. The parents each carry one normal allele and one mutant allele of FGRF3, and they wanted information on their chances of having a homozygous child. The counsellor briefly reviewed the phenotypic features of individuals with achondroplasia. These include facial features (large head with prominent forehead; small, flat nasal bridge; and prominent jaw), very short stature, and shortening of the arms and legs. Physical examination and skeletal X-ray films are used to diagnose this condition. Final adult height is approximately 4 feet. Because achondroplasia is an autosomal dominant condition, a heterozygote has a 1-in-2, or 50%, chance of passing this trait to his or her offspring. However, about 75% of those with achondroplasia have parents of average size who do not carry the mutant allele. In these cases, achondroplasia is due to a new mutation. In the couple being counseled, each individual is heterozygous, and they are at risk for having a homozygous child with two copies of the mutated gene. Infants with homozygous achondroplasia are either stillborn or die shortly after birth. The counselor recommended prenatal diagnosis via ultrasounds at various stages of development. In addition, a DNA test is available to detect the homozygous condition prenatally. Should the parents be concerned about the heterozygous condition as well as the homozygous mutant condition?A couple was referred for genetic counseling because they wanted to know the chances of having a child with dwarfism. Both the man and the woman had achondroplasia (MIM 100800), the most common form of short-limbed dwarfism. The couple knew that this condition is inherited as an autosomal dominant trait, but they were unsure what kind of physical manifestations a child would have if it inherited both mutant alleles. They were each heterozygous for the FGFR3 (MIM 134934) allele that causes achondroplasia. Normally, the protein encoded by this gene interacts with growth factors outside the cell and receives signals that control growth and development. In achrodroplasia, a mutation alters the activity of the receptor, resulting in a characteristic form of dwarfism. Because both the normal and mutant forms of the FGFR3 protein act before birth, no treatment for achrondroplasia is available. The parents each carry one normal allele and one mutant allele of FGRF3, and they wanted information on their chances of having a homozygous child. The counsellor briefly reviewed the phenotypic features of individuals with achondroplasia. These include facial features (large head with prominent forehead; small, flat nasal bridge; and prominent jaw), very short stature, and shortening of the arms and legs. Physical examination and skeletal X-ray films are used to diagnose this condition. Final adult height is approximately 4 feet. Because achondroplasia is an autosomal dominant condition, a heterozygote has a 1-in-2, or 50%, chance of passing this trait to his or her offspring. However, about 75% of those with achondroplasia have parents of average size who do not carry the mutant allele. In these cases, achondroplasia is due to a new mutation. In the couple being counseled, each individual is heterozygous, and they are at risk for having a homozygous child with two copies of the mutated gene. Infants with homozygous achondroplasia are either stillborn or die shortly after birth. The counselor recommended prenatal diagnosis via ultrasounds at various stages of development. In addition, a DNA test is available to detect the homozygous condition prenatally. What if the couple wanted prenatal testing so that a normal fetus could be aborted?Many individuals with metabolic diseases are normal at birth but show symptoms shortly thereafter. Why?2QPEnzymes have all the following characteristics except: a. they act as biological catalysts b. they are proteins c. they carry out random chemical reactions d. they convert substrates into products e. they can cause genetic diseaseQuestions 4 through 6 refer to the following hypothetical pathway in which substance A is converted to substance C by enzymes 1 and 2. Substance B is the intermediate produced in this pathway: a. If an individual is homozygous for a null mutation in the gene that codes for enzyme 1, what will the result be? b. If an individual is homozygous for a null mutation in enzyme 2, what will the result be? c. What if an individual is heterozygous for a dominant mutation in which enzyme 1 is overactive? d. What if an individual is heterozygous for a mutation that abolishes the activity of enzyme 2 (a null mutation)?Questions 4 through 6 refer to the following hypothetical pathway in which substance A is converted to substance C by enzymes 1 and 2. Substance B is the intermediate produced in this pathway: a. If the first individual in Question 4 married the second individual, would their children be able to convert substance A into substance C? b. Suppose each of the adults mentioned in part a was heterozygous for an autosomal dominant mutation that prevents any enzyme function. List the phenotypes of their children with respect to compounds A, B, and C. (Would the compound be in excess, not present, and so on?)6QP7QP8QPa. Compounds A, B, C, and D are known to be intermediates in the pathway for production of protein E. To determine where the block in protein-E production occurred in each individual, the various intermediates were given to each individuals cel Is in culture. After a few weeks of growth with the intermediate, the cells were assayed for the production of protein E. The results for each individuals cells are given in the following table. A plus sign means that protein E was produced after the cells were given the intermediate listed at the top of the column. A minus sign means that the cells still could not produce protein E even after being exposed to the intermediate at the top of the column. Draw the pathway leading to the production of protein E.b. Compounds A, B, C, and D are known to be intermediates in the pathway for production of protein E. To determine where the block in protein-E production occurred in each individual, the various intermediates were given to each individuals cel Is in culture. After a few weeks of growth with the intermediate, the cells were assayed for the production of protein E. The results for each individuals cells are given in the following table. A plus sign means that protein E was produced after the cells were given the intermediate listed at the top of the column. A minus sign means that the cells still could not produce protein E even after being exposed to the intermediate at the top of the column. Denote the point in the pathway in which each individual is blocked.a. If an individual who is homozygous for the mutation found in individual 2 and heterozygous for the mutation found in individual 4 marries an individual who is homozygous for the mutation found in individual 4 and heterozygous for the mutation found in individual 2, what will be the phenotype of their children? b. List the intermediate that would build up in each of the types of children who could not produce protein E.12QPSuppose that in the formation of phenylalanine hydroxylase mRNA, the exons of the pre-mRNA fail to splice together properly and the resulting enzyme is nonfunctional. This produces an accumulation of high levels of phenylalanine and other compounds, which causes neurological damage. What phenotype would be produced in the affected individual?If phenylalanine was not an essential amino acid, would diet therapy (the elimination of phenylalanine from the diet) for PKU work?Phenylketonuria and alkaptonuria are both autosomal recessive diseases. If a person with PKU marries a person with AKU, what will the phenotype of their children be?The normal enzyme required for converting sugars into glucose is present in cells, but the conversion never takes place and no glucose is produced. What could have occurred to cause this defect in a metabolic pathway?Knowing that individuals who are homozygous for the GD allele show no symptoms of galactosemia, is it surprising that galactosemia is a recessive disease? Why?18QPA person was found to have very low levels of functional beta globin mRNA and therefore very low levels of the beta globin protein. What problems would this cause for assembling functional haemoglobin molecules?If an extra nucleotide is inserted in the first exon of the beta globin gene, what effect will it have on the amino acid sequence of the globin polypeptides? Will the globin most likely be fully functional, partly functional, or nonfunctional? Why?Transcriptional regulators are proteins that bind to promoters (the 5-flanking regions of genes) to regulate their transcription. Assume that a particular transcription regulator normally promotes transcription of gene X, a transport protein. If a mutation makes this regulator gene nonfunctional, would the resulting phenotype be similar to a mutation in gene X itself? Why or why not?22QP23QPConsumer products including bandages, cotton balls, diapers, and contact lens solutions are routinely irradiated. There is no opposition to these products in the marketplace. Given this, why are irradiated foods not more accepted when they can prevent illness from E. coli and other pathogens?2EG1CS2CS3CS1QPAchondroplasia is an autosomal dominant form of dwarfism caused by a single gene mutation. Calculate the mutation rate of this gene given the following data: 10 achondroplastic births to unaffected parents in 245,000 births.Why is it almost impossible to directly measure the mutation rates in autosomal recessive alleles?
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