Concept explainers
Although histone modifications can activate or silence genes, these covalent alterations are made to protein molecules involved in nucleosome structure and not to the DNA carrying the activated or silenced allele. If the fixed pattern of active and silenced alleles is to be carried through multiple cell divisions, would you expect the histone modifications to be in cis or trans to the affected alleles? Why?
Hint: This problem involves an understanding of how many copies of each histone are contained in a nucleosome and of the spatial relationship between the histones and the DNA wound around the nucleosome.
To determine: The presence of cis or trans histone modifications in the affected alleles in several cell divisions.
Introduction: The mutation is the change in the nucleotide sequence of the gene, which result in either the formation of a defective protein or no protein at all. The mutation can also alter the regulation of certain genes leading to their hyperactivity or hypoactivity.
Explanation of Solution
The activation of the gene can only take place when the chromatin that contains the gene and its respective regulatory regions to be present in the “open state.” Similarly, for the silencing of the gene, the chromatin containing the gene and its regulatory regions need to be present in a closed state. When these chromatin structures undergo and persist through several cell divisions, the histones that are present in the immediate proximity of the gene, that is cis state will be carrying the histone modifications.
The gene in the chromatin will have to be in a cis state to carry the histone modifications under multiple cell divisions.
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Chapter 19 Solutions
Concepts of Genetics (12th Edition)
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- Duchenne muscular dystrophy (DMD) is an X-linked recessive genetic disease caused by mutations in the gene that encodes dystrophin, a large protein that plays an important role in the development of normal muscle fibers. The dystrophin gene is immense, spanning 2.5 million base pairs, and includes 79 exons and 78 introns. Many of the mutations that cause DMD produce premature stop codons, which bring protein synthesis to a halt, resulting in a greatly shortened and nonfunctionalform of dystrophin. Some geneticists have proposed treating DMD patients by causing the spliceosome to skip the exon containing the stop codon. Exon skipping would produce a protein that is somewhat shortened (because an exon is skipped and some amino acids are missing), but might still result in a protein that had some function (A. Goyenvalle et al. 2004. Science 306:1796–1799). Propose a possible mechanism to bring about exon skipping for the treatment of DMD.arrow_forwardThere are five major types of histones in eukaryotic cells. One of these is not part of the nucleosome core but is thought to participate in locking the two turns of DNA into place. Which histone is this? H2A H4 H3 H1 H2Barrow_forwardWhich of the following does NOT pertain to the myoblast-determining gene 1?*a. It is a master gene.b. It is a silencing gene.c. It produces a transactivating protein.d. It activates its own gene. Gene silencing involves which type of histone modification?* a. acetylation of histone 4 b. dimethylation of histone 3 c. trimethylation of histone 4 d. trimethylation of histone 3 Given the required environment, the totipotency of the nucleus can allow which of the following?* a. a committed cell to undergo dedifferentiation b. a committed cell to undergo terminal differentiation c. a terminally differentiated cell to produce a complete organism d. a terminally differentiated cell to produce specific types of tissues An induced pluripotent cell is described by which of the following?* a. It is a committed cell that undergoes redifferentiation. b. It is a committed cell that undergoes dedifferentiation. c. It is a terminally…arrow_forward
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