Final answer:
A frameshift mutation caused by the insertion of 2 nucleotides leads to a shift in the genetic reading frame, altering the subsequent amino acid sequence and protein function. Insertion of three nucleotides adds only one amino acid and maintains the reading frame, making it less deleterious.
Step-by-step explanation:
The insertion of 2 nucleotides by DNA polymerase leads to a frameshift mutation because it alters the reading frame of the genetic code. The genetic code is read in sets of three nucleotides known as codons, each of which specifies a particular amino acid. If one or two nucleotides are inserted, the reading frame is shifted, and all subsequent codons will be read incorrectly, potentially altering every amino acid that follows the mutation. This usually has a drastic impact on the resulting protein's function. However, the insertion of three nucleotides is often less harmful because it adds just one extra amino acid to the sequence without altering the reading frame of the subsequent codons, thus preserving the integrity of the rest of the protein.