Deoxyribonucleic acid is the genetic material which serves as the template or code for cellular processes in living organisms. DNA is transcribed into messenger ribonucleic acid (mRNA), which is then translated into amino acids, the subunits of the proteins required for life. DNA is constantly subjected to damage by both internal (endogenous) and external (exogenous) assaults. This damage can lead to blocks in transcription and replication or to permanent alterations in the genetic code, and can ultimately lead to disease and death of the organism. It has been reported that up to 90% of human cancers are associated with DNA damage. Because the survival of an organism depends upon precise transcription and replication of its genome, several mechanisms of DNA repair have evolved. In general, these repair systems are universal, correcting defects in the genomes of organisms as diverse as microbes and humans.