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Question 165: "Which of the following DNA lesions will NOT result in a frameshift mutation?"
Answers:
A. 1 Missing base pair
B. 2 Altered base pairs
C. 3 deleted base pairs
D. 2 Inserted base pairs
Answer: "B is correct. MCAT writers love asking questions about frameshift mutations. A frameshift mutation occurs when there is an addition or deletion of 1 or 2 base pairs (a 3 base pair addition or deletion will cause an in-frame mutation, not a frameshift mutation, because each codon is coded by 3 nucleotides), which causes the ribosome to read all downstream codons in the wrong frame. Frameshift mutations usually result in truncated, non-functional proteins.
Altered base pairs (known as point mutations) do not cause the ribosome to read out of frame. Point mutations may cause silent, missense, or nonsense mutations. Answer choices A and C can be eliminated because both are examples of base pair deletion."
Now from that explanation, I see why B would be a correct answer because it is not actually adding or deleting anything. But don't they also state in the explanation that a 3 base pair deletion causes an in-frame mutation, NOT a frameshift mutation? It seems to be that C would also be a correct answer. Am I missing something here?
Answers:
A. 1 Missing base pair
B. 2 Altered base pairs
C. 3 deleted base pairs
D. 2 Inserted base pairs
Answer: "B is correct. MCAT writers love asking questions about frameshift mutations. A frameshift mutation occurs when there is an addition or deletion of 1 or 2 base pairs (a 3 base pair addition or deletion will cause an in-frame mutation, not a frameshift mutation, because each codon is coded by 3 nucleotides), which causes the ribosome to read all downstream codons in the wrong frame. Frameshift mutations usually result in truncated, non-functional proteins.
Altered base pairs (known as point mutations) do not cause the ribosome to read out of frame. Point mutations may cause silent, missense, or nonsense mutations. Answer choices A and C can be eliminated because both are examples of base pair deletion."
Now from that explanation, I see why B would be a correct answer because it is not actually adding or deleting anything. But don't they also state in the explanation that a 3 base pair deletion causes an in-frame mutation, NOT a frameshift mutation? It seems to be that C would also be a correct answer. Am I missing something here?
