Final answer:
The most common source of DNA mutations is replication errors made by DNA polymerase, though these are often corrected by cellular repair mechanisms. Induced mutations result from exposure to mutagens such as chemicals and radiation, which can significantly increase the mutation rate.
Step-by-step explanation:
The most common source of DNA mutation is replication errors; however, these mistakes are typically corrected. During DNA replication, the enzyme DNA polymerase can make mistakes, inserting the wrong nucleotide into the new strand. Although the error rate of DNA polymerase is relatively low, about one incorrect base pair per billion base pairs replicated, it is still the primary source of spontaneous mutations.
Mutations can also be induced by external factors like chemicals and radiation. Such mutations can stem from exposure to mutagens, which include ultraviolet light, X-rays, and chemicals like those found in cigarette smoke. While these factors can increase the mutation rate significantly, it's important to note that not all environmental factors are mutagenic, and the body does have repair mechanisms to fix many of these errors.
Overall, the body's repair mechanisms, such as the base excision repair pathway, are quite effective, correcting more than 99.9% of mistaken base changes to maintain the integrity of the genetic information.