Question

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 cod on. 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? Select all that apply. (Note that two different positions in the codon must be mutated.)
AUC
AUU
AUA
none of these codons

Answer 1

Answer:

none of these codons

Explanation:

In order for mutation to occur to form methionine codon from an isoleucine codon, position 3 must be changed to a G, giving AUG. A secind mutation would then be required at a second site in the AUG codon. since the isoleucine codons, AUA, AUC and AUU does not have a G at position 3, a true reversion can't occur without mutating the position 3 again.