A true reversion occurs when the wild-type DNA sequence is restored to encode its original message by a second mutation at the same site or within the same codon. Which of the following isoleucine codon(s) could be mutated once to form a methionine codon, and then mutated at a second site to restore an isoleucine codon? A. AUC.
B. AUU.
C. AUA.
D. None of these codons.

The correct answer is option d- none of these.

Explanation:

The genetic code for methionne is AUG and genetic code for isoleucine are AUC, AUA, AUU. As we can see that there are first two codons are similar for both methionine and isoleucine.

So mutation at to any other site other than third psostion not possible that can convert isoleucine to methionine and this same mutation site is the only mutation position mutation can revere back methionine to isoleucine.

Thus, none of the given can restore an isoleucine codon.

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