Most mutations occur

• From an incorrect DNA copy

Explanation:

Mutations in the genome can occur due to internal or external factors. The external factor which is called mutagen may be UV light, among several other environmental factors. However, the major cause of mutations is those which are caused by internal factors. Among these internal factors include the incorrect copying of DNA. Replication occurs every second in the cells of our bodies, and this process is error-prone even if exonuclease has the ability to detect mismatches and correct such errors, some go unnoticed and cause mutations which may lead to cancer and other genetic disorders.