ch17 - Chapter 17 17.1 What are CpG islands Of what value...

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Chapter 17 17.1 What are CpG islands? Of what value are CpG islands in positional cloning of human genes? ANS: CpG islands are clusters of cytosines and guanines that are often located just upstream (5 ) from the coding regions of human genes. Their presence in nucleotide sequences can provide hints as to the location of genes in human chromosomes. FEEDBACK: 17.1 DIFFICULTY: easy 17.2. Why is the mutant gene that causes Huntington’s disease called huntingtin? Why might this gene be renamed in the future? ANS: The gene was named huntingtin after the disease that it causes when defective. The gene will probably be renamed after the function of its gene product has been determined. FEEDBACK: 17.1 DIFFICULTY: easy 17.3 How was the nucleotide sequence of the CF gene used to obtain information about the structure and function of its gene product? ANS: The CF gene was identified by map position-based cloning, and the nucleotide sequences of CF cDNAs were used to predict the amino acid sequence of the CF gene product. A computer search of the protein data banks revealed that the CF gene product was similar to several ion channel proteins. This result focused the attention of scientists studying cystic fibrosis on proteins involved in the transport of salts between cells and led to the discovery that the CF gene product was a transmembrane conductance regulator— now called the CFTR protein. FEEDBACK: 17.1 DIFFICULTY: easy 17.4. How might the characterization of the CF gene and its product lead to the
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treatment of cystic fibrosis by somatic-cell gene therapy? What obstacles must be overcome before cystic fibrosis can be treated successfully by gene therapy? ANS: Once the function of the CF gene product has been established, scientists should be able to develop procedures for introducing wild-type copies of the CF gene into the appropriate cells of cystic fibrosis patients to alleviate the devastating effects of the mutant gene. A major obstacle to somatic-cell gene-therapy treatment of cystic fibrosis is the size of the CF gene—about 250 kb, which is too large to fit in the standard gene transfer vectors. Perhaps a shortened version of the gene constructed from the CF cDNA —about 6.5 kb—can be used in place of the wild-type gene. A second major obstacle is getting the transgene into enough of the target cells of the cystic fibrosis patient to alleviate the symptoms of the disease. A third challenge is to develop an expression vector containing the gene that will result in long-term expression of the introduced gene in transgenic cells. Another concern is how to avoid possible side effects caused by overexpression or inappropriate expression of the transgene in cystic fibrosis patients. Despite these obstacles, many scientists are optimistic that cystic fibrosis will be
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ch17 - Chapter 17 17.1 What are CpG islands Of what value...

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