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Ch. 15 - Gene Mutation, DNA Repair, and Transposition
Chapter 15, Problem 25

Imagine yourself as one of the team of geneticists who launches a study of the genetic effects of high-energy radiation on the surviving Japanese population immediately following the atom bomb attacks at Hiroshima and Nagasaki in 1945. Demonstrate your insights into both chromosomal and gene mutation by outlining a short-term and long-term study that addresses these radiation effects. Be sure to include strategies for considering the effects on both somatic and germ-line tissues.

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Identify the types of mutations: Begin by distinguishing between chromosomal mutations (such as deletions, duplications, inversions, and translocations) and gene mutations (such as point mutations, insertions, and deletions) that can result from high-energy radiation exposure.
Design a short-term study: Focus on immediate effects by collecting and analyzing somatic cell samples from survivors to identify chromosomal aberrations using techniques like karyotyping and fluorescence in situ hybridization (FISH).
Plan a long-term study: Investigate germ-line mutations by examining the offspring of survivors for inherited genetic changes. Use whole-genome sequencing to detect subtle gene mutations that may have been passed down.
Consider somatic tissue effects: Evaluate the impact of radiation on somatic tissues by assessing the incidence of cancer and other diseases in the exposed population, using epidemiological studies to track health outcomes over time.
Address germ-line tissue effects: Study the potential for radiation-induced mutations to affect future generations by analyzing reproductive health and genetic disorders in the descendants of those exposed to radiation.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Chromosomal Mutations

Chromosomal mutations involve changes in the structure or number of chromosomes, which can lead to significant genetic disorders or variations. These mutations can result from high-energy radiation causing breaks in DNA strands, leading to deletions, duplications, or translocations of chromosomal segments. Understanding these mutations is crucial for assessing the immediate and long-term impacts of radiation exposure on the population.
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Mutations and Phenotypes

Gene Mutations

Gene mutations are alterations in the nucleotide sequence of a gene, which can affect protein synthesis and function. High-energy radiation can induce point mutations, insertions, or deletions in the DNA sequence, potentially leading to diseases or phenotypic changes. Analyzing gene mutations helps in understanding the molecular basis of radiation effects on individuals and their descendants.
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Somatic vs. Germ-line Effects

Somatic mutations occur in non-reproductive cells and affect only the individual, while germ-line mutations occur in reproductive cells and can be passed to offspring. In studying radiation effects, it is essential to differentiate between these two types of mutations, as somatic mutations may lead to cancer or other health issues in survivors, whereas germ-line mutations can have hereditary implications for future generations.
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Related Practice
Textbook Question

In 2010, a U.S. District Judge ruled to invalidate Myriad Genetics' patents on the BRCA1 and BRCA2 genes. Judge Sweet noted that since the genes are part of the natural world, they are not patentable. Myriad Genetics also holds patents on the development of a direct-to-consumer test for the BRCA1 and BRCA2 genes.

Would you agree with the ruling to invalidate the patenting of the BRCA1 and BRCA2 genes? If you were asked to judge the patenting of the direct-to-consumer test for the BRCA1 and BRCA2 genes, how would you rule?

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Textbook Question

In 2010, a U.S. District Judge ruled to invalidate Myriad Genetics' patents on the BRCA1 and BRCA2 genes. Judge Sweet noted that since the genes are part of the natural world, they are not patentable. Myriad Genetics also holds patents on the development of a direct-to-consumer test for the BRCA1 and BRCA2 genes.

J. Craig Venter has filed a patent application for his 'first-ever human-made life form.' This patent is designed to cover the genome of M. genitalium. Would your ruling for Venter's 'organism' be different from the judge's ruling on patenting of the BRCA1 and BRCA2 genes?

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Textbook Question
Presented here are hypothetical findings from studies of heterokaryons formed from seven human xeroderma pigmentosum cell strains: XP1 XP2 XP3 XP4 XP5 XP6 XP7 XP1 - XP2 - - XP3 - - - XP4 + + + - XP5 + + + + - XP6 + + + + - - XP7 + + + + - - - Note: + = complementation; - = no complementation These data are measurements of the occurrence or nonoccurrence of unscheduled DNA synthesis in the fused heterokaryon. None of the strains alone shows any unscheduled DNA synthesis. Which strains fall into the same complementation groups? How many different groups are revealed based on these data? What can we conclude about the genetic basis of XP from these data?
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Textbook Question
With the knowledge that radiation causes mutations, many assume that human-made forms of radiation are the major contributors to the mutational load in humans. What evidence suggests otherwise?
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Textbook Question
Among Betazoids in the world of Star Trek®, the ability to read minds is under the control of a gene called mindreader (abbreviated mr). Most Betazoids can read minds, but rare recessive mutations in the mr gene result in two alternative phenotypes: delayed-receivers and insensitives. Delayed-receivers have some mind-reading ability but perform the task much more slowly than normal Betazoids. Insensitives cannot read minds at all. Betazoid genes do not have introns, so the gene only contains coding DNA. It is 3332 nucleotides in length, and Betazoids use a four-letter genetic code. The following table shows some data from five unrelated mr mutations. Mutation Description of Mutation Phenotype _ mr-1 Nonsense mutation in codon 829 Delayed-receiver mr-2 Missense mutation in codon 52 Delayed-receiver mr-3 Deletion of nucleotides 83–150 Delayed-receiver mr-4 Missense mutation in codon 192 Insensitive mr-5 Deletion of nucleotides 83–93 Insensitive For each mutation, provide a plausible explanation for why it gives rise to its associated phenotype and not to the other phenotype. For example, hypothesize why the mr-1 nonsense mutation in codon 829 gives rise to the milder delayed-receiver phenotype rather than the more severe insensitive phenotype. Then repeat this type of analysis for the other mutations. (More than one explanation is possible, so be creative within plausible bounds!)
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Textbook Question

Shown here are the amino acid sequences of the wild-type and three mutant forms of a short protein.
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Wild-type: Met-Trp-Tyr-Arg-Gly-Ser-Pro-Thr
Mutant 1: Met-Trp
Mutant 2: Met-Trp-His-Arg-Gly-Ser-Pro-Thr
Mutant 3: Met-Cys-Ile-Val-Val-Val-Gln-His                                  _

Use this information to answer the following questions:

Using the genetic coding dictionary, predict the type of mutation that led to each altered protein.

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