Spontaneous mutations are more rapid in those organisms with very short generation times than in those with long generations. Errors in the DNA replication process happen only about once in 100,000 bases. However, the human genome has about 6 billion bases. DNA repair is also possible. Indeed, it is the rule.
Cells contain several complex systems to fix damage before, during, and after replication.
UV light is a mutagen that you should think about before hitting the beaches or the tanning salons to get your suntan . Somatic mutations early in development may affect the entire development process of the organism. Somatic mutations may result in unusual growth, e.g. cancer. Somatic mutations result in the cells of an individual not being entirely genetically uniform. Mutations in cells destined to produce gametes may occur earlier during development to produce the sex organs or even during meiosis.