High School Biology : Understanding Types of Mutation

Study concepts, example questions & explanations for High School Biology

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Example Questions

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Example Question #1 : Mutation

Which of the following describes a frameshift mutation?

Possible Answers:

Insertion or deletion of a group of nucleotides that is not a multiple of three

Substitution of one nucleotide for another

Insertion or deletion of a group of nucleotides that is a multiple of three

Insertion or deletion of nucleotides that results in a premature stop codon

Correct answer:

Insertion or deletion of a group of nucleotides that is not a multiple of three

Explanation:

A frameshift mutation indicates that the reading frame of the sequence in altered, resulting in production of different codons downstream of the mutation. Because codons are encoded by groups of three nucleotides, a frameshift mutation results from the insertion or deletion of a number of nucleotides that is not a multiple of three.

For example:

ATG-CGT

Add one nucleotide: ATT-GCG-T

Add two nucleotides: ATT-CGC-GT

Add three nucleotides: ATT-CAG-CGT

In the first two additions, there are unpaired nucleotides that will shift the reading frame. In the final addition (three nucleotides), the final group is complete; thus, any codons after the mutation (downstream) will not be affected.

A nonsense involves the addition of a premature stop codon. A missense mutation results in a different codon, and changes the primary structure of the protein. A silent mutation alters the DNA sequence without altering the amino acid result.

Example Question #672 : High School Biology

Which of the following mutations will not result in a change to the amino acid sequence of a protein?

Possible Answers:

Nonsense mutation

Silent mutation

Frameshift mutation

Neutral mutation

Correct answer:

Silent mutation

Explanation:

If a mutation does not alter the amino acid sequence of a protein, it is considered a silent mutation. A neutral mutation changes the amino acid, but not the function of the protein. Both frameshift and nonsense mutations can severely affect the function and structure of a protein.

Example Question #2 : Mutation

Which class of DNA mutation results in the substitution of one amino acid for another in the protein product?

Possible Answers:

Silent

Missense

Frameshift

Nonsense

Correct answer:

Missense

Explanation:

A missense mutation results in the presence of a different amino acid than was encoded by the parental sequence. This type of mutation can have a drastic effect or no effect at all depending on the importance of the amino acid and the type of amino acid that replaces it. Some amino acids are structurally similar and may be able to act as viable substitutes for each other. For example, changing one acidic amino acid to another may ot affect the final protein, but changing a polar amino acid to a nonpolar amino acid will likely disrupt the structure.

A nonsense mutation results in the addition of a premature stop codon, creating a truncated protein product. A silent mutation is a mutation that occurs within the DNA sequence, but does not alter the amino acid sequence. Silent mutations can occur in introns, which are spliced out before translation. Finally, a frameshift mutation is an insertion or deletion of a nucleotide sequence that alters the reading frame of the gene.

Example Question #3 : Mutation

Which of the following is NOT a potential result from a point mutation that substitutes a single nucleotide in a gene?  

Possible Answers:

A codon that codes for a “stop” codon

A codon that codes for the same amino acid as the original sequence

A codon that cannot be transcribed into mRNA 

A codon that codes for a different amino acid

Correct answer:

A codon that cannot be transcribed into mRNA 

Explanation:

A point mutation that substitutes a single nucleotide within a gene alters the three nucleotides that make up an individual codon. There are four possible nucleotides and sixty-four possible codons, formed by 3-nucleotide sequences. Codons code for translation to one of the twenty amino acids. Changing a single nucleotide in the codon can have one of three effects.

First, it can result in a silent mutation. This is a result of the degeneracy of the genetic code, in which multiple codons can code for the same amino acid. Even though the sequence is different, the same amino acid is added. For example, if the sequence is initially CCT it will code for proline. If a mutation changes it to CCC it will still code for proline.

The second option is a missense mutation. In this case, the change in DNA sequence results in a codon for a different amino acid. For example, a mutation from TTT to TCT will change the amino acid from phenylalanine to serine.

Finally, the mutation could change a codon to a stop codon, causing early termination of translation. This is a nonsense mutation. For example, changing the TAT codon for tyrosine to TAA will result in an mRNA stop codon.

No matter how the point mutation affects the final protein product and codon sequence, it will still be transcribed into mRNA.

Example Question #4 : Mutation

Which of the following types of mutation refers to the presence of a premature stop codon?

Possible Answers:

Silent mutation

Radioactive mutation

Missense mutation

Nonsense mutation

Frameshift mutation

Correct answer:

Nonsense mutation

Explanation:

A nonsense mutation results in a stop codon. This can be the result of an insertion or a deletion, causing a change in the DNA sequence from a normal amino acid codon to one of the three possible stop codon sequences.

A missense mutation changes the identity of a codon from one amino acid to another, resulting in a change to the protein primary structure. A silent mutation occurs when a mutation does not change the amino acid coded for by that codon. A frameshift mutation is an insertion or deletion that changes the reading frame of the entire protein and can have severe detrimental effects. A radioactive mutation is not a specific classification of mutations. 

Example Question #5 : Mutation

Scientists were examining the maize genome. They had two specimens: one control and one specimen that had undergone mutagenesis. They saw that the mutant specimen underwent a knockout caused by a nucleotide switch in the DNA. Is this a dominant or recessive mutation?

Possible Answers:

Sex linked dominant

Recessive 

Cannot be determined 

Dominant

Sex linked recessive 

Correct answer:

Dominant

Explanation:

This mutation is dominant because whatever mutation occurred at the genomic level was sufficient to cause an amino acid switch, i.e., it was expressed. If this were recessive, we would see that the nucleotide base change would not have yielded a knock out. Recall that only one copy of a "bad" gene is required for it to be expressed if it is a dominant mutation, whereas two copies of the "bad" gene are required for it to be expressed if it is a recessive mutation. No information is provided to consider sex linked traits.

Example Question #6 : Mutation

Scientists were examining the maize genome. They had two specimens: one control and one specimen that had undergone mutagenesis. They saw that the mutant specimen underwent a knockout caused by a nucleotide switch in the DNA.  However, when they compared gene sequences, they saw no change in size. Which type of mutation had most likely occurred?

Possible Answers:

Nonsense mutation

Insertion

Frameshift 

Deletion 

Substitution

Correct answer:

Substitution

Explanation:

The problem states that there was no change in gene size between the two specimens. That means that the mutant and the control still had the same number of nucleotide bases. Out of all options provided, substitution is the only possible type of mutation that fulfills the description. Deletion, insertion, nonsense and frameshift mutations would have all lead to a size discrepancy. 

Example Question #7 : Mutation

The starting sequence of a gene changed from AUGTTCGACGTG to AUGTTTCGACGTG. What type of mutation is this?

Possible Answers:

Missense mutation

Frameshift mutation

Translocation

Point mutation

Correct answer:

Frameshift mutation

Explanation:

The change introduces an extra "T' near the beginning of the sequence. This mutation will change the frame of the codons of the gene, and result in a frameshift mutation.

Example Question #8 : Mutation

Scientists studying the genetics of a congenital disease analyzed the chromosomes of the patient and found a large portion of chromosome twenty-three in chromosome one, and a small part of chromosome one in chromosome twenty-three. What is this an example of?

Possible Answers:

Deletion

Inversion

Duplication

Translocation

Correct answer:

Translocation

Explanation:

Translocation is when two different chromosomes exchange large parts of the genetic sequence. 

Example Question #9 : Mutation

A single nucleotide polymorphism changes one nucleotide in a gene sequence. As a result, the gene gains a stop codon 500 base pairs to soon and the protein—when it is translated—is truncated or cut short. Which of the following types of mutations did the point mutation cause?

Possible Answers:

Missense mutation

Insertion

None of these

Nonsense mutation

Frameshift mutation

Correct answer:

Nonsense mutation

Explanation:

A nonsense mutation arises when a point mutation in DNA causes a mRNA strand to have a stop codon prematurely. It changes a base that would have led to an amino acid to a base that makes that triplet codon to a stop codon. This causes the ribosome to stop making the protein too soon and results in a shorter protein. The name arises from the drastic effect this has on the function of the protein. 

While biologically important, the other choices are incorrect. An insertion mutation changes the number of bases in that segment of DNA—extra is base added. On the other hand, a missense mutation switches one amino acid for another in that sequence. Last, a frameshift mutation changes the reading frame of three codons. So if a gene in DNA has the following sequence (keeping in mind that there are two strands not one):

ACTATTCCCGGATTC 

The resulting RNA sequence would be as follows:

UGAUAAGGGCCUAAG

A frameshift mutation would occur if a mutation caused thymine to be inserted into the first codon in the following DNA sequence:

ATCTATTCCCGGATTC

As a result, the resulting mRNA sequence would be the following:

UAGAUAAGGGCCUAAG

The entire reading frame has been changed. Because they have been moved over by one base all the triplet have been changed; therefore, each triplet is off by one base.

 

 

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