ABSTRACT
This chapter describes a logical progression, beginning with the causes of mutations and then moving on to the ways in which mutations are repaired. Mutations arise in two ways: Some mutations are spontaneous errors in replication that evade the proofreading function of the DNA polymerases that synthesize new polynucleotides at the replication fork. Other mutations arise because a mutagen has reacted with the parent DNA, causing a structural change that affects the base-pairing capability of the altered nucleotide. Many chemicals that occur naturally in the environment have mutagenic properties and these have been supplemented in recent years with other chemical mutagens that result from human industrial activity. Physical agents such as radiation are also mutagenic. Direct repair mechanisms are important, but they form a very minor component of the overall repertoire of repair processes available to most organisms. Excision repair systems are much more prevalent and are able to correct a much broader range of mutations.
