Answer:
Single nucleotide deletion
Step-by-step explanation:
Original DNA sequence: 
A T A C G G T A 
T A T G C C A T 
 
Mutated DNA sequence: 
A T C G G T A G 
T A G C C A T C 
 
In the mutated sequence, there is a nucleotide missing. It goes from ATACGGTA to ATCGGTAG. The A nucleotide is gone. This represents a single base pair deletion. 
Even though it is only one base, this changes the way the entire sequence is interpreted. The DNA transcribed into an mRNA and then translated into a protein by reading triplet codons which correspond to specific amino acids.
So while the initial sequence would be read as:
ATA, CGG, TA...
The new sequence would be read as:
ATC, GGT, AG...
So the sequence of the protein is completely altered.