Chapter 15 Gene Mutation, DNA Repair, and Transposition PDF

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Chapter 15 Gene Mutation, DNA Repair, and Transposition 1) Mutations that arise in nature, from no particular artificial agent, are called ________. A) natural mutations B) induced mutations C) spontaneous mutations D) chromosomal aberrations E) cosmic mutations Answer: C Section: 15.1, 15.2 2) Nutritional mutations can be defined as ________. A) those mutations that do not allow an organism to grow on minimal medium but do allow growth on complete medium B) those mutations that change the composition of the medium C) those mutations belonging to the group called prototrophs D) those mutations caused by site-specific mutagenesis E) all strains that are not auxotrophic Answer: A Section: 15.1 3) Conditional mutations are more likely to result from a mutation caused by which of the following alterations to the coding region of a gene? A) four bases added within a short region of a gene B) base addition C) X-rays D) deletion E) tautomeric shift Answer: E Section: 5.1 4) Two formal terms used to describe categories of mutational nucleotide substitutions in DNA are ________. A) base analogs and frameshift B) error prone and spontaneous C) transversions and transitions D) euchromatic and heterochromatic E) sense and antisense Answer: C Section: 15.1 5) Which of the following name two mutagens that would be classified as base analogs? A) acridine orange and proflavin B) ethylmethane sulfonate and ethylmethylketone peroxide C) ultraviolet light and cosmic radiation D) 5-bromouracil and 2-aminopurine E) hydroxyurea and peroxidase Answer: D Section: 15.3 6) A class of mutations that results in multiple contiguous amino acid changes in proteins is likely to be which of the following? A) base analog B) transversion C) transition D) frameshift E) recombinant

Answer: D Section: 15.1 7) Ultraviolet light causes pyrimidine dimers to form in DNA. Some individuals are genetically incapable of repairing some dimers at “normal” rates. Such individuals are likely to suffer from ________. A) xeroderma pigmentosum B) SCID C) phenylketonuria D) muscular dystrophy E) Huntington disease Answer: A Section: 15.5 8) Transposons, or jumping genes, are DNA elements that move within the genome. In which organismic groups are transposons found? A) bacteria B) eukaryotes C) mammals D) ancient bacteria E) all organismic groups Answer: E Section: 15.8 9) All insertion sequences (IS elements) contain two features that are essential for their movement. What are these two elements? A) transposase and inverted terminal repeats B) integrase and pseudogenes C) integrase and oncogenes D) proto-oncogenes and oncogenes E) transposase and oncogenes Answer: A Section: 15.8 10) Some bacterial transposons, known as Tn elements, are larger than insertion sequences (IS elements) and contain protein-coding genes that have human health significance. What might such a bacterial transposon contain? A) drug resistance B) oncogene C) pseudogene D) proto-oncogene E) dissociation element Answer: A Section: 15.8 11) Barbara McClintock discovered mobile elements in corn by analyzing the genetic behavior of two elements, Ds and Ac. The interplay between these two elements has become one of the most interesting stories of discovery in the field of genetics. How do Ds and Ac interact? A) Ds causes a deletion next to the insertion site of Ac. B) Ac causes a deletion next to the insertion site of Ds. C) While Ds moves only if Ac is present in the genome, Ac is capable of autonomous movement. D) The movement of Ac is dependent on two forms of Ds. E) Both elements can move only within chromosome 9. Answer: C Section: 15.8 12) DNA may be damaged from the by-products of normal cellular aerobic respiration. Name three of these electrophilic oxidants that are generally classified as reactive oxidants. Answer: superoxides(O2-), hydroxyl radicals (·OH), and hydrogen peroxide (H2O2) Section: 15.2

13) Describe the mutagenic action of the following two mutagens: 5-bromouracil and ultraviolet light. Answer: The mutagen 5-bromouracil is an analog of thymine, which anomalously pairs with guanine. Ultraviolet light causes thymine dimers. Section: 15.3 14) Some mutagens cause genetic changes that can be “corrected” by reexposing cells to the same mutagen. Other mutagens do not behave in this way. Provide one example of each of these two types of agents and describe the mutational changes caused in DNA. Explain why some mutagens behave in one way, while others do not. Answer: Mutagens that cause base substitutions are “corrected” by mutagens of the same class (nitrous acid, 2-aminopurine, and 5-bromouracil). Frameshift mutations are “corrected” by the same class of frameshift mutagens, but not by mutagens that cause base substitutions. X-rays cause major structural changes in chromosomes (deletions, translocations, etc.) and are not “corrected” by any mutagen, including X-rays. Section: 15.1, 15.2, 15.3 15) It has been found that a particular “+ -” combination of frameshift mutations in gene X gives a wild-type phenotype, whereas a “- +” combination gives a mutant phenotype, even though the sites of insertion/deletion are the same. How might these results be explained? Answer: A frameshift in the “+ -” direction may have introduced a nonsense triplet, which was not introduced, by chance, by the opposite “- +” combination. Section: 15.1, 15.3, 15.4 16) Mutations may exert a variety of effects on living systems. List at least three categories of mutations based on their biological effects. Answer: morphological mutations, nutritional or biochemical mutations, behavioral mutations, regulatory mutations, lethal mutations, conditional mutations Section: 15.1 17) Under certain conditions, the rate of mutation of a particular gene may be determined in humans. Which four properties of the mutation would favor the most direct determination of mutation rate in humans? Answer: dominant, fully expressed, 100% penetrant, single locus Section: 15.4 18) In a survey of 240,000 human births, six achondroplastic births were recorded to parents who were unaffected. Given that this form of dwarfism is caused by a fully penetrant, dominant, autosomal gene, what is the mutation rate? Answer: 6/(4.8 × 105) Section: 15.4 19) Three human disorders—fragile-X syndrome, myotonic dystrophy, and Huntington disease— are conceptually linked by a common mode of molecular upset. Describe the phenomena that link these disorders. Answer: All three are caused by disparate genes, but each gene was found to contain repeats of a unique trinucleotide sequence. In addition, the number of repeats may increase in each subsequent generation (genetic anticipation). Section: 15.4 20) What is meant by the term photoreactivation repair? Answer: Photoreactivation repair, discovered in 1949, is a process described in E. coli in which UV-induced DNA damage can be partially reversed if cells are briefly exposed to light in the blue range of the visible spectrum. Section: 15.5 21) List five general categories of mutation. Answer: induced, spontaneous, morphological, nutritional/biochemical, behavioral, regulatory, lethal, conditional Section: 15.1

22) Considering the electromagnetic spectrum, identify likely mutagens from the following list: radio waves, microwaves, infrared, ultraviolet, X-rays, gamma rays, cosmic rays. Answer: ultraviolet, X-rays, gamma rays, cosmic rays Section: 15.3 23) Under which condition(s) might one have an amino acid substitution in a protein that does not result in an altered phenotype? Answer: The possibility of a change in protein function, therefore phenotype, depends on the location and chemical properties of the involved amino acid(s). Section: 15.1 24) Recent discoveries on causes of fragile-X syndrome, myotonic dystrophy, and Huntington disease indicate which type of genetic alteration? Answer: changes in trinucleotide repeats Section: 15.4 25) What is the Ames test, and how does it work? Answer: Four tester strains of Salmonella typhimurium are used to test for sensitivity and specificity of mutagenesis. Section: 15.6 26) What is the common influence of ultraviolet light on DNA? Answer: generation of pyrimidine dimers Section: 15.3 27) Describe the phenomenon of photoreactivation repair. Answer: Photoreactivation repair is mediated by the photoreactivation enzyme (PRE), which cleaves covalent bonds between the dimers. Section: 15.5 28) The process of error correction of mismatched bases carried out by DNA polymerases is called ________. Answer: proofreading Section: 15.5 29) Recombinational repair is activated when damaged DNA has escaped repair and the distortion disrupts the process of replication. Which gene is responsible recombinational repair? Answer: recA Section: 15.5 30) Which human condition is caused by unrepaired UV-induced lesions? Answer: xeroderma pigmentosum Section: 15.5 31) When X-rays penetrate cells, electrons are ejected from atoms of molecules. Stable molecules can be transformed into which two types of hazardous materials? Answer: free radicals and reactive ions Section: 15.3 32) How was it determined that X-rays are mutagenic? Answer: H. J. Muller determined that a direct relationship occurred between X-linked recessive lethals and X-ray dose in Drosophila. Section: 15.1 33) A mutation that occurs naturally, without exposure to a known mutagen, is called a(n) ________. Answer: spontaneous mutation Section: 15.2 34) Three major types of RNAs are mRNA, rRNA, and tRNA. For each of the conditions below predict the consequences in terms of the population of proteins being synthesized in a particular cell. What qualitative and quantitative changes, if any, are expected in the individual protein involved (if one is involved) and in the population of proteins produced in that cell?

(a) An frameshift mutation in mRNA. The condition is heterozygous in the involved cell. (b) A deletion (homozygous) that removes approximately half of the rRNA genes. Answer: (a) Population of proteins: Half of the protein products of that gene will be defective, and the other half will be normal. Individual protein: The protein should show multiple amino acid substitutions “downstream” from the point of the mutation. If a nonsense triplet is introduced, the protein would be shortened in the substituted region. (b) Population of proteins: There would be an overall reduction in protein synthesis. Individual protein: All of the proteins would be made in their normal form, but at reduced levels. Section: 15.1 35) Assume that a new mutation occurs in the germ line of an individual. What finding would suggest that the new mutation is dominant rather than recessive? Answer: If dominant and if passed to the next generation, it would be expressed. New recessive mutations are not normally expressed in the next generation unless, through a combination with a like mutation from the other parent, they are homozygous. Section: 15.1 36) Apurinic sites (AP sites) involve a spontaneous loss of a(n)________ in an intact double-helix DNA molecule. Answer: purine Section: 15.2 37) One type of mutation involves the replacement of a purine with a purine, while another causes the replacement of a pyrimidine with a purine. What general terms are associated with these two mutational phenomena? Answer: transition and transversion, respectively Section: 15.1 38) In general, mutation rates in humans occur in the range of ________(frequency) per gamete per generation. Answer: 10-5 to 10-6 Section: 15.1 39) Assuming one mutational event in a gene, on average, which of the following mutagens or mutational conditions would be expected to cause the most damage to a protein synthesized by such a mutagenized gene: 5-bromouracil, 2-amino purine, ethylmethane sulfonate, or frameshift? Answer: frameshift Section: 15.3 40) Describe the action of the enzyme transposase. Answer: Transposase makes staggered cuts in chromosomal DNA, into or out of which an IS element can insert. Section: 15.8 41) How were insertion sequences (IS elements) first discovered? Answer: IS elements were first discovered during the analysis of mutations in the gal operon of E. coli. Section: 15.8 42) What are LINES? Answer: LINES are long interspersed elements of about 1 to 6 kb in length that are plentiful (about 850,000 copies) in the human genome. Section: 15.8 43) Of the two cell lines that can contain a mutation in an organism, somatic and germ line, the latter is more consequential to subsequent generations. Answer: TRUE Section: 15.1, 15.8

44) Certain base analogs such as 5-bromouracil cause mutations by chemically altering nitrogenous bases in nonreplicating DNA. Answer: FALSE Section: 15.3 45) When treating an organism with a mutagen, although it is possible that homozygous mutations will occur, it is more likely that most new mutations will be heterozygous or hemizygous. Answer: TRUE Section: 15.3 46) The shorter the wavelength of a radiation source, the greater its likelihood of causing damage. Answer: TRUE Section: 15.3 47) 2-amino purine is an alkylating agent. Answer: FALSE Section: 15.3 48) Although mutation is the original source of genetic variation, its influence on changing allelic frequencies is relatively minor. Answer: TRUE Section: 15.1 49) Pyrimidine dimers are typically caused by the mutagen 2-amino purine. Answer: FALSE Section: 15.3 50) A missense mutation causes premature chain (protein) termination. Answer: FALSE Section: 15.4 51) Strand discrimination during the process of DNA repair is based on DNA methylation in E. coli. Answer: TRUE Section: 15.5 52) Postreplication repair is a system that responds after damaged DNA has escaped repair and failed to be completely replicated. Answer: TRUE Section: 15.5 53) Loss-of-function mutations that eliminate the function of a gene product are also known as null mutations or gene knockouts. Answer: TRUE Section: 15.7 54) IS elements (insertion sequences) are stable DNA occupants of prokaryotic genomes that are not found among eukaryotes. Answer: FALSE Section: 15.8...