Genetic Code

If the second base is changed from a U to an A, the resulting codon is 5'-UAG-3' which is a stop codon. Mutations that result in stop codons are called nonsense mutations.

A base substitution involves the substitution of one nucleotide for another, and effects the coding of a single codon. An insertion/deletion mutation involves the addition of an extra nucleotide into a sequence or the removal of a nucleotide from a sequence. An insertion/deletion mutation can change the entire reading frame of a genetic sequence, affecting the coding of every codon in that sequence.

The mutation is a frameshift mutation from the deletion of a C.