Concept explainers
Dominant mutations can be categorized according to whether they increase or decrease the overall activity of a gene or gene product. Although a loss-of-function mutation (a mutation that inactivates the gene product) is usually recessive, for some genes, one dose of the normal gene product, encoded by the normal allele, is not sufficient to produce a normal
Want to see the full answer?
Check out a sample textbook solutionChapter 22 Solutions
Concepts of Genetics (12th Edition)
- 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…arrow_forwardExplain the difference between a gain-of-function mutation and a dominant-negative mutation.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_forward
- Two methods for functionally inactivating a gene without altering the gene sequence involve dominant negative alleles and RNA interference (RNAi). Describe how each method can inhibit expression of a gene.arrow_forwardExposure to various chemicals can cause DNA mutations. Classify the examples as representative of transition, transversion, or nsertion/deletion mutations. Transition replacement of T:A: with C:G treatment with nitrogen mustard causes this type of mutation oxidative deamination via nitrous acid causes this type of mutation treatment with 5-bromouracil causes the replacement of A:T with G:C Transversion replacement of G:C with T:A Answer Bank Insertion/Deletion the removal of one or more base pairs treatment with proflavin causes this type of mutationarrow_forwardBRCA1 is mutated in a large percentage of hereditary breast and ovarian cancers. BRCA1 protein serves as a key enzyme in repairing DNA double-strand breaks. More than 800 mutations in the BRCA1 are clinically significant. This collection of mutations include missense mutations, small deletions, and large rearrangements that result in a protein with reduced function or no protein product. BRCA1 functions by interacting with a variety of proteins, such as Rb, Myc, cyclin-dependent kinase (CDK), and Rad50/51. Rb is important for cell cycle arrest; Myc is a transcription factor that activates genes required for cell proliferation; activated CDK promotes cell cycle progression; and Rad50/51 proteins facilitate repair of DNA double-strand breaks. How many of the mutations listed below would lead to excessive cell growth when the cell was either homozygous or heterozygous for the mutation? Increased expression of Myc Constitutively active Rad50/51 A null mutation in Rb Continuous production…arrow_forward
- Duchenne Muscular Dystrophy (DMD) is a disorder that primarily affects the function of skeletal muscles used for movement and cardiac muscles used for heart beating. Dystrophin is a protein encoded by a single gene, DMD, that is expressed in skeletal and cardiac muscle. Some forms of muscular dystrophy may be caused by different mutations in the DNA sequence of the DMD gene. Because the DMD locus is on the X chromosome, males are affected at higher rates. Two brothers, one of whom has DMD and one of whom does not, worked with their genetic counselor (Links to an external site.) to have their DMD gene sequenced to identify genetic variation that may explain why one brother was affected and the other not. Because DMD is a very long gene, a fictionalized, simplified model of the results is presented here (Figure 1). The actual DMD mRNA is about 16,000 base-pairs!------Consider single nucleotide polymorphism (SNP) #1 (Figure 1). Is this mutation likely to cause Duchenne muscular…arrow_forwardHuntington disease (HD) is an inherited neurodegenerative disorder characterized by gradual, irreversible impairment of psychological, motor, and cognitive functions. Symptoms typically appear in middle age, but onset can occur at almost any age, and the course of the disease can range from 15 to 20 years. The molecular basis of HD is becoming better understood, and the genetic mutation has been traced to a gene that encodes a large protein of unknown function. In individuals who will not develop HD, a region of the gene that encodes the N-terminus of this protein has a sequence of CAG codons (for glutamine) repeated 6 to 39 times in succession. In individuals with adult-onset HD, this codon (3 nucleotides) is typically repeated 40 to 55 times In those with childhood-onset HD, it is repeated more than 70 times. *codon: refers to the 3 nucleotides that code for amino acid. A small portion of the coding sequence of the HD gene is given below. The nucleotide sequence of the DNA is…arrow_forwardResearchers have identified a gene in humans that (when mutated) causes tremors and unstable walking due to neurological problems. This disorder is inherited in an autosomal recessive manner, and the mutant allele isknown to result from a loss-of-function mutation. The same gene hasbeen found in mice, although a mutant mouse version has not beendiscovered. To develop an effective drug therapy to treat this disorderin humans, it would be experimentally useful to have a mouse model.In other words, it would be desirable to develop a strain of mice thatcarry the mutant allele in the homozygous condition. How would youdevelop such a strain?arrow_forward
- Discuss the consequences of a germ-line versus a somatic mutation.arrow_forward1). In the absence of this enzyme, a substance called ceroid lipofuscin accumulates in lysosomes in the brain, resulting in seizures, blindness, decline in cognitive function and motor skills, dementia, and death by the late teens or early 20’s. The TPP1 gene is 6695 bp in length. Think about the characteristics of Batten disease, and then suggest an approach to gene therapy that might be effective for this specific genetic disorder. You may assume that your research team is working in the U.S. and your research is funded by a grant from the National Institutes of Health (NIH). Please EXCLUDE the use of CRISPR from consideration. A. Will you use germline or somatic cell gene therapy? Please NAME and DEFINE the form of gene therapy selected, then explain WHY this is the most appropriate choice.arrow_forward1). In the absence of this enzyme, a substance called ceroid lipofuscin accumulates in lysosomes in the brain, resulting in seizures, blindness, decline in cognitive function and motor skills, dementia, and death by the late teens or early 20’s. The TPP1 gene is 6695 bp in length. Think about the characteristics of Batten disease, and then suggest an approach to gene therapy that might be effective for this specific genetic disorder. You may assume that your research team is working in the U.S. and your research is funded by a grant from the National Institutes of Health (NIH). a) Hypothetically, what specific type of VECTOR will you use to perform your gene therapy? Please select from the following list of potential vectors: disabled retrovirus, adenovirus, adeno-associated virus (AAV), or herpes simplex virus (HSV), then give two reasons why this specific vector is the most appropriate for your gene therapy. Please explain why you were able to rule out the other potential…arrow_forward
- Human Anatomy & Physiology (11th Edition)BiologyISBN:9780134580999Author:Elaine N. Marieb, Katja N. HoehnPublisher:PEARSONBiology 2eBiologyISBN:9781947172517Author:Matthew Douglas, Jung Choi, Mary Ann ClarkPublisher:OpenStaxAnatomy & PhysiologyBiologyISBN:9781259398629Author:McKinley, Michael P., O'loughlin, Valerie Dean, Bidle, Theresa StouterPublisher:Mcgraw Hill Education,
- Molecular Biology of the Cell (Sixth Edition)BiologyISBN:9780815344322Author:Bruce Alberts, Alexander D. Johnson, Julian Lewis, David Morgan, Martin Raff, Keith Roberts, Peter WalterPublisher:W. W. Norton & CompanyLaboratory Manual For Human Anatomy & PhysiologyBiologyISBN:9781260159363Author:Martin, Terry R., Prentice-craver, CynthiaPublisher:McGraw-Hill Publishing Co.Inquiry Into Life (16th Edition)BiologyISBN:9781260231700Author:Sylvia S. Mader, Michael WindelspechtPublisher:McGraw Hill Education