Suppose that a single DNA base change of an A to a T occurs

Suppose that a single DNA base change of an A to a T occurs and is copied during replication. Is this change necessarily a mutation?

Solution

Yes this change is mutation in DNA sequence. This substitution of A with T will cause change in the codon of mRNA transcribed. If the sequence in DNA is ATG , it will be transcribed into codon UAC, but due to substitution of A to T base sequence in DNA will change to TTG, which will reanscribe into codon AAC.