Question

Hydroxylamine is a chemical mutagen that causes, specifically, GC-to-AT transitions in phage T4, while 5-bromouracil readily causes both types of transitions. UV light causes an increase in the frequency of rII mutations in T4. Most, 57 of 62 analyzed, of these UV-induced mutations revert at a high frequency when exposed to 5-bromouracil but not when exposed to hydroxylamine. The remaining 5 mutations reverted with both mutagens. What type of mutation does UV mainly create when producing rII mutants?

A-to-C

C-to-A

G-to-A

A-to-G

G-to-C

Answer 1

UV light primarily causes GC-to-AT transition mutations in phage T4, as indicated by the high reversal rate of UV-induced mutations with 5-bromouracil and the low reversal with hydroxylamine.

Step-by-step explanation:

UV light primarily induces pyrimidine dimers, which are a common type of mutation where adjacent thymine bases pair with each other, forming abnormal covalent bonds. Given that most of the UV-induced mutations in phage T4 revert in the presence of 5-bromouracil but not with hydroxylamine, it suggests that UV mainly creates GC-to-AT transition mutations. This is because hydroxylamine specifically causes such transitions while 5-bromouracil can cause transitions at AT base pairs or GC base pairs. Therefore, if the majority of mutations revert with 5-bromouracil but not hydroxylamine, they are likely GC-to-AT transitions. The UV-induced mutations which reverted with both mutagens suggest that there may also be a minority of AT-to-GC transitions.