Question

Ochre and amber are two types of nonsense mutations. Before the genetic code was worked out, Sydney Brenner, Anthony O. Stretton, and Samuel Kaplan applied different types of mutagens to bacteriophages in an attempt to determine the bases present in the codons responsible for amber and ochre mutations. They knew that ochre and amber mutants were suppressed by different types of mutations, demonstrating that each is a different termination codon. They obtained the results. A single‑base substitution could convert an ochre mutation into an amber mutation. Hydroxylamine induced both ochre and amber mutations from wild‑type phages. 2‑aminopurine caused ochre to mutate to amber. Hydroxylamine did not cause ochre to mutate to amber. These data do not allow the complete nucleotide sequence of the amber and ochre codons to be worked out, but they do provide information about the bases found in the nonsense mutations. What conclusion about the bases in the codons of amber and ochre mutations can be made from these observations

Answer 1

Answer:

On the basis of the given information, the actions imparted by hydroxylamine results in GC to AT transition, while 2-aminopurine provides both GC to AT and AT to GC transition. In the given question, the mutagenic effects of hydroxylamine and 2-aminopurine are mentioned.  

The hydroxylamine induces both amber and ochre mutations from wild-type phages. Therefore, amber and ochre codons must comprise uracil and/or adenine. The amber mutations are produced from ochre codon by 2-aminopurine, however, not by hydroxylamine. This demonstrates that ochre mutations do comprise adenine and uracil and amber mutations comprise guanine, and can also possess either uracil and/or adenine.