The correct answer is insertion
Insertion can be defined as the addition of one or more nucleotide base pairs into a DNA sequence. It can leads to change in the codon sequence of a DNA, known as frameshift mutation as it changes the order of nucleotide sequence that codes for a specific protein. By this way, it can be detrimental as it leads to formation of non-functional or mutated protein.
As in the mutated sequence shows addition of four extra guanine bases (ATCGGGGGGATCCT) in the original sequence (ATCGGGATCCT), it represents the insertion mutation.
