Question

The image shows an example of a deletion mutation.
An original D-N-A strand reads C-T-G-G-A-G with the first two G's crossed out. The mutated D-N-A strand reads C-T-A-G.

When did the mutation most likely occur?

Responses

A. before transcription

deletion mutations occur when DNA is not copied properly during DNA replication, which occurs prior to transcription.
A. before transcription deletion mutations occur when DNA is not copied properly during DNA replication, which occurs prior to transcription.

B. during transcription

deletion mutations occur prior to, not during, transcription.
B. during transcription deletion mutations occur prior to, not during, transcription.

C. during translation

deletion mutations occur during DNA replication, prior to transcription and translation, not during translation.
C. during translation deletion mutations occur during DNA replication, prior to transcription and translation, not during translation.

D. after translation

deletion mutations occur during DNA replication, prior to, not after, transcription and translation.
D. after translation deletion mutations occur during DNA replication, prior to, not after, transcription and translation.

Answer 1

A. before transcription

Deletion changed the DNA sequence itself, so it most likely arose during DNA replication (S phase) — before transcription and translation. Transcription and translation use the DNA/mRNA templates; they don't create permanent DNA deletions.