A missense mutation in Neurospora will revert by treatment with nitrous acid,but not by hydroxylamine.Hydroxylamine (HA)causes only G·C → A·T transitions,while nitrous acid causes both G·C → A·T and A·T → G·C transitions.The original mutation (not the reversion)must have been:
A)AT to CG.
B)AT to GC.
C)AT to TA.
D)GC to AT.
E)GC to TA.

Question

Quizplus · Accepted Answer

The original mutation must have been GC to AT because nitrous acid, which can cause both G·C → A·T and A·T → G·C transitions, can revert it, indicating the mutation involved a G·C to A·T change. Hydroxylamine, which only causes G·C → A·T transitions, cannot revert it, suggesting the mutation did not involve a G·C to A·T change.

A Missense Mutation in Neurospora Will Revert by Treatment with Nitrous