Multiple Choice
Which type of mutation most directly stops translation of an mRNA by introducing a premature stop codon in the coding sequence?
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17. Mutation, Repair, and Recombination
Types of Mutations
Multiple Choice
Which of the following is a point mutation (not a frameshift mutation)?
A
Deletion of two nucleotides in the coding sequence, shifting the reading frame
B
Insertion of one nucleotide in the coding sequence, shifting the reading frame
C
Insertion of three nucleotides in the coding sequence, shifting the reading frame
D
A single-nucleotide substitution that changes one codon to another (missense mutation)
Verified step by step guidance1
Understand the difference between point mutations and frameshift mutations. Point mutations involve a change in a single nucleotide, such as substitution, while frameshift mutations involve insertions or deletions that alter the reading frame of the genetic sequence.
Analyze each option to determine if it causes a frameshift or is a point mutation. Remember that insertions or deletions of nucleotides not in multiples of three cause frameshifts, while changes involving a single nucleotide substitution do not shift the reading frame.
For the deletion of two nucleotides, recognize that since two is not a multiple of three, this will shift the reading frame, making it a frameshift mutation.
For the insertion of one nucleotide, similarly, since one is not a multiple of three, this will also cause a frameshift mutation.
For the insertion of three nucleotides, note that three nucleotides correspond to one codon, so this insertion does not shift the reading frame and is not a frameshift mutation. However, it is not a point mutation either, as it involves adding nucleotides rather than substituting one.
Finally, identify that a single-nucleotide substitution changes one codon to another without altering the reading frame, which classifies it as a point mutation (specifically a missense mutation).
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