Spontaneous mutations are naturally occurring changes in the DNA sequence that arise without any external influence. These mutations often result from intrinsic cellular processes, such as errors during DNA replication, spontaneous chemical changes in nucleotide bases, or structural instability of the DNA molecule. One major source of spontaneous mutations is DNA replication errors, where DNA polymerase incorporates an incorrect nucleotide during the replication process. Although proofreading mechanisms exist, occasional mismatches escape correction, leading to permanent base pair changes in the daughter strand. Tautomeric shifts are another form of spontaneous mutation, where a nucleotide base transiently adopts an alternative chemical form, such as keto-enol or amino-imino forms. These rare tautomeric states can pair incorrectly during replication, causing point mutations. Depurination is also significant, involving the spontaneous loss of purine bases (adenine or guanine) from the DNA backbone, creating apurinic sites. If these sites are not repaired, DNA polymerase may insert an incorrect nucleotide opposite the vacant position, leading to mutations. Collectively, these spontaneous mechanisms contribute to the natural background rate of genetic