In the Ames test, what happens when his- bacteria are exposed to a chemical and experience a higher level of growth than the control?
A) The his- bacteria now utilized histidine from the media.
B) The reversion rate is lower than seen for spontaneous mutations.
C) The his- bacteria utilized DNA repair tools to fix the mutation.
D) A reversion mutation allowed the his- bacteria to regain their ability to make histidine (revert to his+).
E) The tested chemical is regarded as a non-mutagen.
Answer: D
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