Genetic Analysis: An Integrated Approach (3rd Edition)
3rd Edition
ISBN: 9780134605173
Author: Mark F. Sanders, John L. Bowman
Publisher: PEARSON
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Chapter 11, Problem 39P
Thinking back to the discussion of gain
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Leber Congenital Amaurosis (LCA) causes progressive vision loss due to defects in the gene that encodes RPE65 isomerase. Affected individuals are homozygous recessive for mutant alleles of the RPE65 gene. You are trying to determine the molecular nature of the mutations in three individuals with LCA. For ease of analysis, you may assume that each individual is homozygous for the same mutant allele (though the three individuals have different mutations than each other). You use the polymerase chain reaction to amplify DNA from each patient and you determine the sequence of the DNA and compare it to unaffected individuals. You identify the following differences. Note that the non-template strand of DNA is given and the changes are highlighted using red boldface. You can assume that the sequences are in the first reading frame (eg. the first three nucleotides of each sequence is a codon). The coding region of the gene is 1602 bp and the position of the sequences shown below is…
Recall that Leber congenital amaurosis (LCA), a formof congenital blindness in humans, can be caused byhomozygosity for recessive mutations in the RPE65gene. Recently, a rare dominant mutation in RPE65has been implicated as one cause of an eye diseasecalled retinitis pigmentosa, which is characterized byretinal degeneration that can progress to blindness.The dominant RPE65 mutation is a missense mutation causing amino acid 447 in the polypeptide tochange from Asp to Glu. Little is known about thenature of the mutant protein.a. Do you think that the dominant allele is morelikely a loss-of-function or a gain-of-functionmutation? Explain.b. As described in this chapter, gene therapy for LCAhas been at least partially successful. Do you thinkthat the same kind of gene therapy can be used forpatients with retinitis pigmentosa caused by thedominant mutant allele of RPE65? Explain.
Leber congenital amaurosis (LCA) is a form of congenital blindness in humans and is known to be caused by homozygosity for recessive mutations in the RPE65 gene. Recently, a rare dominant mutation in RPE65 has been implicated as one cause of an eye disease called retinitis pigmentosa, which is characterized by retinal degeneration that can progress to blindness. The dominant RPE65 mutation is a missense mutation causing amino acid 447 in the polypeptide to change from Asp to Glu. Little is known about the nature of the mutant protein.
a. Do you think that the dominant allele is more likely a loss-of-function or a gain-of-function mutation? Explain.
b. Recently a group of clinicians and scientists reported that gene therapy (gene replacement therapy) for LCA has been at least partially successful. Do you think that the same kind of gene therapy can be used for patients with retinitis pigmentosa caused by the dominant mutant allele of RPE65? Explain.
Chapter 11 Solutions
Genetic Analysis: An Integrated Approach (3rd Edition)
Ch. 11 - 11.1 Identify two general ways chemical mutagens...Ch. 11 - 11.2 Nitrous acid and (BU) alter DNA by different...Ch. 11 - 11.3 What is the difference between a transition...Ch. 11 - What is the difference between a synonymous...Ch. 11 - 11.5 UV irradiation causes damage to bacterial...Ch. 11 - Ultraviolet (UV) radiation is mutagenic.
What...Ch. 11 - Researchers interested in studying mutation and...Ch. 11 - The effect of base - pair substitution mutations...Ch. 11 - Describe the purpose of the Ames test. How are...Ch. 11 - 11.10 In numerous population studies of...
Ch. 11 - 11.11 Two different mutations are identified in a...Ch. 11 - What is the phenotype effect of inserting a Ds...Ch. 11 - 11.13 Answer the following questions concerning...Ch. 11 - Several types of mutation are identified and...Ch. 11 - 11.15 A sample of the bacterium is exposed to...Ch. 11 - 11.16 A strain of is identified as having a null...Ch. 11 - Describe the difference between DNA transposons...Ch. 11 - 11.18 How are flanking direct repeat sequences...Ch. 11 - 11.19 Using the adeninethymine base pair in this...Ch. 11 - The partial amino acid sequence of a wild-type...Ch. 11 - Prob. 21PCh. 11 - 11.22 Many human genes are known to have homologs...Ch. 11 - The fluctuation test performed by Luria and...Ch. 11 - In this chapter, three features of genes or of DNA...Ch. 11 - Briefly compare the production of DNA double -...Ch. 11 - During mismatch repair, why is it necessary to...Ch. 11 - 11.27 Following the spill of a mixture of...Ch. 11 - 11.28 In an Ames test using Salmonella bacteria a...Ch. 11 - A wild - type culture of haploid yeast is exposed...Ch. 11 - A fragment of a wild - type polypeptide is...Ch. 11 - Prob. 31PCh. 11 - Alkaptonuria is a human autosomal recessive...Ch. 11 - 11.33 In an experiment employing the methods of...Ch. 11 - Using your knowledge of DNA repair pathways choose...Ch. 11 - 11.35 Ataxia telangiectasia is a human inherited...Ch. 11 - A geneticist searching for mutations uses the...Ch. 11 - 11.37 In a mousebreeding experiment a new mutation...Ch. 11 - 11.38 Considering the Dumbo mutation in a Problem,...Ch. 11 - 11.39 Thinking back to the discussion of...Ch. 11 - 11.40 Common baker’s yeast () is normally grown at...Ch. 11 - 11.41 The two gels illustrated below contain...
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- Name three different types of loss of function mutations and in each case explain how the mutation exerts a loss of function effect on a genearrow_forwardProvide one example of a clinical implication of a “silent mutation” that proven to have an effect on the phenotype and provide a brief description of its molecular characteristics?arrow_forwardWhich form of Retinoblastoma typically results in unilateral disease and exhibits 2-hit mutational kinetics?arrow_forward
- Diamond–Blackfan anemia (DBA) is a rare, dominantgenetic disorder characterized by bone marrow malfunction,birth defects, and a predisposition to certaincancers. Infants with DBA usually develop anemia in the firstyear of life, have lower than normal production of red blood cellsin their bone marrow, and have a high risk of developing leukemiaand bone cancer. At the molecular level, DBA is causedby mutations in any one of 10 genes that encode ribosomalproteins. The first-line therapy for DBA is steroid treatment,but more than half of affected children develop resistance tothe drugs and in these cases, treatment is halted. DBA can betreated successfully with bone marrow or stem cell transplantsfrom donors with closely matching immune system markers.Transplants from unrelated donors have significant levels ofcomplications and mortality. While a stem cell transplant from an unaffected donor is currentlythe only cure for DBA, genome-editing technologies mayone day enable the correction of…arrow_forwardDiamond–Blackfan anemia (DBA) is a rare, dominantgenetic disorder characterized by bone marrow malfunction,birth defects, and a predisposition to certaincancers. Infants with DBA usually develop anemia in the firstyear of life, have lower than normal production of red blood cellsin their bone marrow, and have a high risk of developing leukemiaand bone cancer. At the molecular level, DBA is causedby mutations in any one of 10 genes that encode ribosomalproteins. The first-line therapy for DBA is steroid treatment,but more than half of affected children develop resistance tothe drugs and in these cases, treatment is halted. DBA can betreated successfully with bone marrow or stem cell transplantsfrom donors with closely matching immune system markers.Transplants from unrelated donors have significant levels ofcomplications and mortality. Given that a faulty ribosomal protein is the culprit and causesDBA, discuss the possible role of normal ribosomal proteins.Why might bone marrow cells be…arrow_forwardExplain the difference between a gain-of-functionmutation and a dominant-negative mutation. Why areboth these types of mutation usually dominant?arrow_forward
- Discuss the consequences of a germ-line versus a somatic mutation.arrow_forwardTwo possible point mutations are the substitution of lysine for leucine or the substitution of serine for threonine. Which is likely to be more serious and why?arrow_forwardSilent mutations that occur in DNA are quite common in living cells and usually involve no effects onphenotype. 1) Provide one example of a clinical implication of a “silent mutation” that proven to have an effect on the phenotype and provide a brief description of its molecular characteristics?arrow_forward
- Two related forms of muscular dystrophy—Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD)—are both recessive, X-linked, single-gene conditions caused by point mutations, deletions, and insertion in the dystrophin gene. Each mutated form of dystrophin is one allele. Of the two diseases, DMD is much more severe. Given your knowledge of mutations, the genetic code, and translation, propose an explanation for why the two disorders differ greatly in severity.arrow_forwardThe table below shows different types of mutations in different positions in four genes. Choose the letter (A to E), from the drop-down menu, that represents the most likely type of protein that will be produced from each of these mutated genes. A: completely normal protein B: functional protein with ONE amino acid different from normal C: non-functional protein with ONE amino acid different from normal D: non-functional protein with MANY amino acids different from normal E: no protein at all Answer Type of mutation Position of mutation in gene (A, B, C, D, or E) before the part of the gene that specifies the active site of the enzyme 2 base pair insertion Inonsense immediately before the stop codon in the part of the gene that specifies the active site of the enzyme silent 1 base pair insertion in an intronarrow_forwardThe genetic alteration responsible for sickle-cell anemia in humans involves: a transition mutation from A to G, substituting glutamic acid for valine in a-globin a transversion mutation from T to A, substituting valine for glutamic acid in b-globin a transition mutation from T to C, substituting valine for glutamic acid in b-globin a transversion mutation from G to C, substituting glutamic acid for valine in a-globin a frameshift mutation of one ATC codon, removing glutamic acid from b-globinarrow_forward
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