Concept explainers
CASE STUDY|A mysterious muscular dystrophy
A man in his early 30s suddenly developed weakness in his hands and neck, followed a few weeks later by burning muscle pain–all symptoms of late-onset muscular dystrophy. His internist ordered genetic tests to determine whether he had one of the inherited muscular dystrophies, focusing on Becker muscular dystrophy, myotonic dystrophy Type I, and myotonic dystrophy Type II. These tests were designed to detect mutations in the related dystrophin, DMPK, and ZNF9 genes. The testing ruled out Becker muscular dystrophy. While awaiting the results of the DMPK and ZNF9 gene tests, the internist explained that the possible mutations were due to expanded tri- and tetranucleotide repeats, but not in the protein-coding portion of the genes. She went on to say that the resulting disorders were due not to changes in the encoded proteins, which appear to be normal, but instead to altered RNA splicing patterns, whereby the RNA splicing remnants containing the
How does this contrast with other types of muscular dystrophy, such as Becker muscular dystrophy and Duchenne muscular dystrophy?
Want to see the full answer?
Check out a sample textbook solutionChapter 15 Solutions
Essentials of Genetics Plus Mastering Genetics with eText -- Access Card Package (9th Edition) (Klug et al. Genetics Series)
- 6a. Given the following mutated sequence (with respect to the normal sequence), what TYPE of mutation occurred: AAGCTTACarrow_forwardFriedreich ataxia (FRDA) is an autosomal recessive, neurodegenerative disease that causes a lack of voluntary coordination of muscle movements. Affected individuals are homozygous for an unusually large number (expansion) of repeats of a trinucleotide sequence (GAA) in the first intron of the X25 gene. Unaffected individuals typically have between 7 and 38 repeats of the trinucleotide (GAAGAAGAAGAA…). FRDA patients have anywhere from 66 to over 1,700 repeats. To understand how the GAA trinucleotide expansion leads to FRDA, researchers looked at X25 gene expression by extracting RNA from affected and unaffected patients and doing a northern blot analysis (see the figure below): In panel “a,” the researchers used a probe to detect X25 mRNA. In panel “b,” the researchers used a probe on a duplicate of the original blot to detect human GAPDH mRNA (GAPDH is an enzyme involved in glycolysis). The sample labeled “YR” is mRNA from yeast cells that was used as a control. Explain…arrow_forwardQuestion:- Often a given mutation or variant will have slightly different phenotypes in different groups of patients. “Genetic Background” is frequently used to explain how the same exact mutation could exhibit different phenotypes in different populations. Please explain.arrow_forward
- 6a. Given the following mutated sequence (with respect to the normal sequence), what TYPE of mutation occurred: AAGCTTAC 6b. Where did the mutation take place?arrow_forwardCh. 18-2 The photos shown below illustrate a case of synpolydactyly, a genetic abnormality characterized by two phenotypes: partially or completely duplicated fingers or toes, and webbing between fingers or toes. The same mutations that give rise to the human phenotype also give rise to a similar phenotype in mice. In which family of genes do you think these mutations occur?arrow_forward8a. Given the following mutated sequence (with respect to the normal sequence), what TYPE of mutation occurred: AAACGTTAC 8b. Where did the mutation take place?arrow_forward
- 33. For the following gene, which type of regulatory sequence has likely been deleted in mutant 1?arrow_forwardTwo 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_forward1. a)What would happen if the aminoacyl tRNA synthetase responsible for charging alanine tRNAs also charged methionine tRNAs with alanine? b)What would happen if an individual was homozygous for mutant alleles of the gene encoding the aminoacyl tRNA synthetase responsible for charging leucine tRNAs?arrow_forward
- Huntington disease (HD) can arise from a rare, short, in-frame addition of CAG nucleotide triplets within the huntingtin (HTT) gene coding region, which creates a disease-causing allele with the symptoms only appearing later in life. Using this information, describe an experiment that could be undertaken to determine whether a currently healthy young individual is a carrier of the HD-causing mutation. Describe the method you would use and how you would interpret the results of this experiment.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_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). Other scientists have suggested that it might be possible to use CRISPR to treat this genetic disorder in affected individuals. (i) First, what is CRISPR? (BRIEFLY describe what it is and how it works). (ii) Briefly describe how CRISPR could be utilized in treating genetic conditions such as Batten disease.arrow_forward
- Biology: The Dynamic Science (MindTap Course List)BiologyISBN:9781305389892Author:Peter J. Russell, Paul E. Hertz, Beverly McMillanPublisher:Cengage LearningBiology 2eBiologyISBN:9781947172517Author:Matthew Douglas, Jung Choi, Mary Ann ClarkPublisher:OpenStax