Genetics : DNA Mutations, Damage, and Repair Mechanisms

Study concepts, example questions & explanations for Genetics

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Example Questions

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Example Question #1 : Dna Mutations, Damage, And Repair Mechanisms

Which of the following represents a frameshift mutation to the given template strand?

5'-AGCCTTAGC-3'

Possible Answers:

5'-AGCGCTTAGC-3'

5'-CTTAGC-3'

5'-AGCCTTAGG-3'

5'-TGCCTTAGC-3'

5'-TTTAGCCTTAGC-3'

Correct answer:

5'-AGCGCTTAGC-3'

Explanation:

A frameshift mutation results in a change of the codon reading frame and results from the addition or deletion of a set of nucleotides that is not a multiple of three. If a mutation occurs that is a multiple of three, the reading frame is unchanged and a simple addition or deletion has occurred.

Template:               5'-AGC-CTT-AGC-3' 

Frameshift mutant:  5'-AGC-GCT-TAG-C-3' 

Point mutant:          5'-TGC-CTT-AGC-3'

Point mutant:          5'-AGC-CTT-AGG-3'

Deletion:                5'-CTT-AGC-3'

Insertion:               5'-TTT-AGC-CTT-AGC-3'

Note that all except the frameshift mutation contain sets of three nucleotides to create triplets. The frameshift leaves a singular, un-grouped cytosine.

Example Question #2 : Dna Mutations, Damage, And Repair Mechanisms

What is the name of the enzyme that unwinds the DNA for replication?

Possible Answers:

DNA polymerase II

DNA polymerase I

DNA gyrase

DNA ligase

DNA helicase

Correct answer:

DNA helicase

Explanation:

DNA helicase is responsible for breaking bonds between base pairs in the DNA thus unwinding it for replication.

Example Question #3 : Dna Mutations, Damage, And Repair Mechanisms

Which of the following statements is not true about genetic mutations?

Possible Answers:

Mutations can have no effect on the function of the protein product.

Mutations can cause a gain-of-function of the protein product.

A mutation can be inherited. 

Some mutations can cause lethality.

All mutations cause a loss-of-function of the protein product.

Correct answer:

All mutations cause a loss-of-function of the protein product.

Explanation:

Mutations can cause a huge variety of effects, including proteins that don't work (loss-of-function) and proteins that are too active (gain-of-function). Not all mutations are loss-of-function. Mutations can be inherited or from environmental factors, and many times a mutation will mean nothing at all for the organism. 

Example Question #4 : Dna Mutations, Damage, And Repair Mechanisms

A(n) __________ mutation causes a gene to have a premature stop codon. This means that translation of the protein will never be complete, because the machinery stops too early.

Possible Answers:

duplication

point

nonsense

inversion

missense

Correct answer:

nonsense

Explanation:

A nonsense mutation will cause the protein to never be completed because of a premature stop codon, hence the protein "never makes sense," ie nonsense. Missense will make a protein with the incorrect amino acid sequence. A point mutation can cause a nonsense mutation, but is not the best answer, as it is vague. The other two mutations also theoretically can cause a nonsense mutation, but nonsense is most specific answer. 

Example Question #5 : Dna Mutations, Damage, And Repair Mechanisms

Methylation and Acetylation are the main components of which non mutation protein change?

Possible Answers:

single nucleotide polymorphism

copy number variation

non-coding RNA

epigenetics

Correct answer:

epigenetics

Explanation:

Epigenetic deals with which genes are expressed and which are repressed. Genes are turned on or off via methylation or acetylation of the histone wrapping the DNA. Single nucleotide polymorphism is an inherited single nucleotide change at a specific position of the genome, contributing to risk factors or being a modifier to a disease. Copy number variation are the repeats of sequence in the genome and the number of repeats vary for each individual. Non-coding RNA refers to RNA that is not translated into a protein.

Example Question #6 : Dna Mutations, Damage, And Repair Mechanisms

What refers to chromosomes in which the centromere is off to one side?

Possible Answers:

lop-centric

acrocentric

metacentric

sub-metacentric

Correct answer:

sub-metacentric

Explanation:

Sub-metacentric is when the the centromere is off to one side. Metacentric is when the centromere is in the middle. Acrocentric is when the centromere is at one end. Lop-centric is not a real thing.

Example Question #7 : Dna Mutations, Damage, And Repair Mechanisms

What term describes the structural abnormalities where one chromosome arm is deleted and there is duplication of the other, resulting in mirror images?

Possible Answers:

inversion

ring chromsome

translocation

isochromosome

Correct answer:

isochromosome

Explanation:

Isochromosome is when one arm is deleted and the other arm is copied to make the second arm a copy of the first. Translocation is an even exchange of information between non-homologous chromosomes. Inversion is when a piece of a chromosome switches direction or is reversed. Ring chromosome is when the telomeres are the end of a chromosome are cleaved off and the remaining chromosomal ends join forming a ring.

Example Question #8 : Dna Mutations, Damage, And Repair Mechanisms

If a cell senses a harmful mutation and ultimately decides to undergo apoptosis, which signal will the cell release which is a pro-apoptotic factor?

Possible Answers:

Bcl-2

Bcl-xl

Mcl-1

BAX

Correct answer:

BAX

Explanation:

BAX is pro- apoptotic along with BID. BAK, BAD.  Bcl-2, Bcl-XI, Mcl-1 are all anti-apoptotic. This is important in the mitochondrial death pathways.

Example Question #1 : Dna Mutations, Damage, And Repair Mechanisms

Xeroderma pigmentosum is a disease where there are 7 mutated genes which were caused by UV damage. Which process of the DNA repair mechanism is defective?

Possible Answers:

genomic instability

homologous recombination repair

nucleotide excision repair

DNA mismatch repair

Correct answer:

nucleotide excision repair

Explanation:

Nucleotide excision repairs refers to short sequences of DNA being removed and repaired with the undamaged strand. It is usually removing bulky adducts on DNA, mostly thymine dimers which are caused by UV radiation. DNA mismatch repair is fixing a single mismatched DNA. Homologous recombination repair is fixing a double stranded break and using the sister chromosome as a template. These are mostly autosomal recessive disorders. Genomic instability simply refers to the high number of mutation which leads to instabilities in the genome. 

Example Question #2 : Dna Mutations, Damage, And Repair Mechanisms

What pair of chromosomes are mutated when a child exhibits down syndrome characteristics?

Possible Answers:

21

25

2

18

Correct answer:

21

Explanation:

The correct answer here is 21. Remember that we can begin by excluding the option that is 25 because there are only 23 pairs of chromosomes in a human being. If you chose any of the other options, remember that down syndrome is also called trisomy 21. This is a syndrome where the 21st pair of chromosomes has a third mutation on it. 

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