Flexi Says: Scientists have estimated that up to one million DNA changes per day can occur in the genome of a single human cell. These changes result from all types of environmental factors, including UV radiation, as well as factors that occur within normal cell processes. However, most of these changes are repaired by the cell. Estimates of changes that become permanent mutations range from 1 x 10-4 to 1 x 10-6 mutations per gene. This means that a mutation would be expected for every 1,000 to 1,000,000 copies of a gene.