Errors in DNA Replication
The low overall rate of mutation during DNA replication (1 base pair change in one billion base pairs per replication cycle) does not reflect the true number of errors that take place during the replication process. The number is kept so low by a proof-reading system that checks newly synthesized DNA for errors and corrects them when they are found. Errors in DNA replication can take different forms, but usually revolve around the addition of a nucleotide with the incorrect base, meaning the pairing between the parent and daughter strand bases is not complementary. The addition of an incorrect base can take place by a process called tautomerization. A tautomer of a base group is a slight rearrangement of its electrons that allows for different bonding patterns between bases.