Looking for Quiz 16 :
Gene Regulation in Eukaryotes Ii: Epigenetics
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As you may have noticed in the data table of Figure 16.14, the daughters whose fathers were exposed to X-rays were less likely to produce any offspring than the control daughters (whose fathers were not exposed to X-rays). Among 1015 daughters whose fathers had been exposed to X-rays, only 783 produced offspring. By comparison, among 1011 control daughters, 947 were able to produce offspring. Suggest reasons why the daughters of irradiated fathers appear less likely to produce any offspring than the control daughters.
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Daughters from fathers who were exposed to X-rays are infertile because there is possibility of lethal mutation in sperm due to irradiation which in turn was passed on to the daughters.
Hence, the females with ClB chromosome from their mothers and an X chromosome from their irradiated fathers will be infertile. It is due to the mutations that are passed on to the ClB daughters from the father.
As the mutations make the daughters infertile the reason behind this is that these mutations affect the production of ova in these females and make them infertilE.Hence, the control daughters whose fathers were not exposed to irradiation were more fertile when compared with the daughters with the fathers who were exposed to X-rays.
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Nonsense suppressors, which are described in solved problem S1, tend to be very inefficient at their job of allowing readthrough of a stop codon. How would it affect the cell if they were efficient at their job
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The nonsense suppressors tend to be very inefficient by allowing read through of a stop codon in some cases.
If they are efficient, the peptide elongation would be terminated. The cell growth would be terminated because of the genes which have stop codons. There would be regular release factors and these appropriate release factors get associated with ribosome.
The inefficient nonsense suppressors which allow the read through the stop codons would waste the energy of the cell. The resulting protein will not be fully functional some times.
The suppression will be effective if the suppressor tRNA is charged with the correct amino acid and if the amount of tRNA or its concentration in the cell is sufficient. The efficiency of the suppressor also depends upon its context, of the base on 3'end of the codon.
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Researchers were interested in whether two different chemicals were mutagens. Let's call them chemical A and chemical B. They followed the protocol described in the experiment of Figure 16.12 and obtained the following results:
Would you conclude that chemical A or chemical B (or both) is a mutagen Explain.
Would you conclude that chemical A or chemical B (or both) is a mutagen Explain. Free
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The ClB daughters whose fathers were exposed to Chemical B produced more number of tubes that lacked male offspring. So, chemical B can be considered as a mutagen. The control ones produced only three tubes out of 2,108. When this number is compared with the number produced by chemical B, (77 out of 4,203) it can be very well concluded as a mutagen.
The ClB daughters, whose fathers were exposed to chemical A, produced two test tubes which lacked male offspring. The ratio was two out of 1,402. This number is very close to the control ones which is three out of 2,108. Hence, chemical A cannot be considered as a mutagen.
The percentage of ClB daughters (whose fathers were exposed to chemical B) who could not produce sons is much higher than the contol ones. So, chemical B is a mutagen.
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In E. coli , a variety of mutator strains have been identified in which the spontaneous rate of mutation is much higher than in normal strains. Make a list of the types of abnormalities that could cause a strain of bacteria to become a mutator strain. Which abnormalities do you think would give the highest rate of spontaneous mutation
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How would each of the following types of mutations affect the amount of functional protein that is expressed from a gene
A. Nonsense
B. Missense
C. Up promoter mutation
D. Mutation that affects splicing
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What does a suppressor mutation suppress What is the difference between an intragenic and an intergenic suppressor
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Discuss the times in a person's life when it would be most important to avoid mutagens. Which parts of a person's body should be most protected from mutagens
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The Luria-Delbrück fluctuation test is consistent with the random mutation theory. How would the results have been different if the physiological adaptation hypothesis had been correct
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A large amount of research is aimed at studying mutation. However, there is not an infinite amount of research money. Where would you put your money for mutation research
A. Testing of potential mutagens
B. Investigating molecular effects of mutagens
C. Investigating DNA repair mechanisms
D. Some other place
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In Chapters 12 through 16, we discussed many sequences that are outside the coding sequence and are important for gene expression. Look up two of these sequences and write them out. Explain how a mutation could change these sequences, thereby altering gene expression.
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A gene mutation changes an AT base pair to a GC pair. This causes a gene to encode a truncated protein that is nonfunctional. An organism that carries this mutation cannot survive at high temperatures. Make a list of all the genetic terms that could be used to describe this type of mutation.
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In the experiment of Figure 16.14, the ClB chromosome carries a large paracentric inversion, in which the centromere is found outside of the inverted region. This inversion prevents crossing over with the other X chromosome (which may carry an X-ray-induced lethal mutation). Does a paracentric inversion really prevent crossing over Explain. You may wish to review Chapter 8 to answer this question.
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Lactose permease is encoded by the lacY gene of the lac operon. A mutation occurred at codon 64 that changed the normal glycine codon into a valine codon. The mutant lactose permease is unable to function. However, a second mutation, which changes codon 50 from an alanine codon to a threonine codon, is able to restore function. Are the following terms appropriate or inappropriate to describe this second mutation
A. Reversion
B. Intragenic suppressor
C. Intergenic suppressor
D. Missense mutation
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For each of the following mutations, is it a transition, transversion, addition, or deletion The original DNA strand is
5 -GGACTAGATAC-3
(Note: Only the coding DNA strand is shown.)
A. 5 -GAACTAGATAC-3
B. 5 -GGACTAGAGAC-3
C. 5 -GGACTAGTAC-3
D. 5 -GGAGTAGATAC-3
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Explain how the technique of replica plating supports a random mutation theory but conflicts with the physiological adaptation hypothesis. Outline how you would use this technique to show that antibiotic resistance is due to random mutations.
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X-rays strike a chromosome in a living cell and ultimately cause the cell to die. Did the X-rays produce a mutation Explain why or why not.
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In Muller's experiment with ClB chromosomes, is the experiment measuring the mutation rate within a single gene Explain. If we divide 91 by 783, we obtain a mutation rate of 11.6%. In your own words, explain what this value means.
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How would you modify the Ames test to discover physical mutagens Would it be necessary to add the rat liver extract Explain why or why not.
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Are each of the following mutations silent, missense, nonsense, or frameshift mutations The original DNA strand is 5 -ATGGGACTAGATACC-3 . (Note: Only the coding strand is shown; the first codon is methionine.)
A. 5 -ATGGGTCTAGATACC-3
B. 5 -ATGCGACTAGATACC-3
C. 5 -ATGGGACTAGTTACC-3
D. 5 -ATGGGACTAAGATACC-3
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From an experimental point of view, is it better to use haploid or diploid organisms for mutagen testing Consider both the Ames test and the experiment of Figure 16.14 when preparing your answer.
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