What enzyme or function is being affected in mutant (a), causing many mismatched base pairs?

DNA polymerase is the enzyme that is responsible for adding correct nucleotide pairs to new and growing DNA strands. Mismatched base pair errors will occur if this enzymes is not able to function optimally. There are other system that work DNA polymerase, these are proof reading system and mismatch repair system. Less than optimum function of these system will lead to uncorrected mismatched base pairs.