Hypermutation

Hypermutation is a modification of a DNA sequence that occur very frequently in the genome, and these mutations are spontaneous errors that occur during replication, because they´re caused by incorrect repair of mismatches.

Hypermutation can also happens by deamination of cytosine bases to produce uracil, followed by excision of the uracil by glycosylase to form AP sites. On the next replication, a nucleotide is inserted at opposite AP site and after another replication, the mutation is stabilized.

This mutation occurs in some vertebrates, including humans, to generate a diverse range of immunoglobulin proteins to deal with all possible antigens.  These point mutations happen, for example, in the V (variable) gene region of an immunoglobulin gene that encode the antigen-binding sites, resulting in the amino acid modification in the heavy and light chain of the antibody V regions. So, these regions are responsible for the affinity maturation and specificity required to produce effective neutralizing antibodies.