Question 1

a)A met⁺ strain of Neurospora was treated with a mutagen to create met^- mutants.The mutants were reverted to met⁺ with HA (hydroxylamine),which causes GC to AT transitions.What was the original mutation on the molecular level? b)Two of the revertants showed odd results when crossed with a wild-type met⁺ strain. $$\begin{array} { l l } \text { Cross } & \text { Progeny } \ \text { met } ^ { + } \text {revertant A } \times m et ^ { + } \text {wild type } & 8 8 \% \text { met }^+ \ & 12 \% \text { met }^- \end{array}$$ $\begin{array}{ll} \text { met }^{+} \text {revertant B } \times \text { met }^{+} \text {wild type }& 93 \% \text { met }^{+}\ &7\% \text { met }^- \end{array}$ Explain how these results occurred and why the above numbers of offspring were obtained.

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Question 2

Some indel mutations can be created spontaneously as a result of errors during DNA replication.
a)Use diagrams to show how 1)insertions and 2)deletions are spontaneously created as a result of the replication of tandem repeats.
b)Give the term used to describe this process.
c)Name two human diseases that arise as a consequence of expanded trinucleotide repeats in DNA.
d)Describe two ways in which expanded trinucleotide repeats can cause disease.

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Question 3

Five different mutations were derived from base pair substitutions at a single codon.In this codon,the mutant alleles had arginine,leucine,glycine,serine,and cysteine.What was the wild-type codon?

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Question 4

How do mutation and DNA damage differ?

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Question 5

Consider the following mutations and,for each,explain whether you expect it to be
a)potentially promoting cancer
b)dominant or recessive
i)a mutation that destroys the active site of an enzyme necessary to promote cell cycle
ii)a very premature STOP codon in a gene encoding a protein involved in the excision-repair mechanism
iii)a point mutation that renders constitutively active one of the signaling proteins in the Ras pathway
iv)a null mutation in a gene encoding an apoptotic (apoptosis-promoting)protein

Accepted Answer

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Question 6

Crossing over is a very precise process.Why is it important that the process of crossing over is so precise? What impact would there be if it were not precise? Draw a picture depicting an imprecise crossover and show the result of this imprecise event.

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Question 7

Photoreactivation repair is effective only in the presence of visible light.What other repair mechanism is available to repair pyrimidine dimers if visible light was not available? Describe the steps of this mechanism.

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The answer of Photoreactivation repair is effective only in the...

Question 8

5-Bromouracil is an analog of thymine that normally pairs with adenine.Its rare tautomeric form pairs with adenine.Show the steps (i.e.,several replications)by which 5-bromouracil causes the GC base pair shown below to change to an AT base pair.Show the point at which the rare tautomeric form of 5-bromouracil occurs.Show both products of all divisions in which 5-bromouracil is involved.Do not show chemical structures.

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The answer of 5-Bromouracil is an analog of thymine that...

Question 9

Three mutations were obtained in a bacterial gene.An antibody is available for the protein product of this gene.Both Northern analysis (RNA separated by electrophoresis,blotted,and probed with DNA)and Western analysis (proteins separated by  electrophoresis,blotted,and probed with antibodies)were performed on the mutants.The results are summarized below.  
For each mutation,what kind of mutation occurred and how do you know it?
a)Mutant 1 b)Mutant 2 c)Mutant 3

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The answer of Three mutations were obtained in a bacterial...

Question 10

Both cytosines and 5' methyl-cytosines are susceptible to spontaneous deamination,which leads to GT to AT transitions.Do you expect cytosine nucleotides to be a "hot spot" for spontaneous mutations? Briefly explain your answer.

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Question 11

Match between columns
                        Premises:  alkylation of G residues
 depurination
 pyrimidine dimers
 deamination
 double-stranded breaks

Accepted Answer

The Answer of photolyase and base-excision repair and SOS repair is...

Question 12

Match between columns
                        Premises:  2-aminopurine
 UV light
 acridine orange
 aflatoxin
 ethylmethanesulfonate (EMS)

Accepted Answer

The Answer of Single-nucleotide insertions or deletions resulting in frameshift is...

Question 13

Match between columns
                        Premises:  missense mutation
 silent mutation
 frameshift mutation
 nonsense mutation
 synonymous mutation
 nonsense suppressor mutation

Accepted Answer

The Answer of a mutation that changes UUA to UUG is...

Quiz 16: Mutation, Repair, and Recombination

Five different mutations were derived from base pair substitutions at a single codon.In this codon,the mutant alleles had arginine,leucine,glycine,serine,and cysteine.What was the wild-type codon?

How do mutation and DNA damage differ?

Crossing over is a very precise process.Why is it important that the process of crossing over is so precise? What impact would there be if it were not precise? Draw a picture depicting an imprecise crossover and show the result of this imprecise event.

Photoreactivation repair is effective only in the presence of visible light.What other repair mechanism is available to repair pyrimidine dimers if visible light was not available? Describe the steps of this mechanism.

Both cytosines and 5' methyl-cytosines are susceptible to spontaneous deamination,which leads to GT to AT transitions.Do you expect cytosine nucleotides to be a "hot spot" for spontaneous mutations? Briefly explain your answer.

Match all repair systems that can repair (or play a role in the repair of) that particular type of damage.

Match all descriptions that apply to that type of mutagen. Note that each statement may be used more than once and each type of mutation may have more than one correct statement.

Match each mutation with statement(s) that apply to that type of mutation. Note that each statement may be used more than once and each type of mutation may have more than one correct statement.