The building blocks of genes are the nucleotides (chemically speaking, these are bases plus a sugar-phosphate that serves to link the bases). They are arranged in specific orders in each gene. If, in the course of cell reproduction, one nucleotide is substituted for another, a nucleotide is accidentally deleted, or an extra nucleotide is added, this is called a spontaneous mutation. If that mutation occurs in a germ (egg or sperm) cell, that mutation can be inherited by the next generation.¹

The creation of energy in a cell utilizes oxygen. In addition to energy, that process produces toxic byproducts called reactive oxygen species a class of free radicals, which can damage DNA, as well as cellular proteins and fats.²

Ultraviolet light has been recognized as a cause of DNA damage for nearly 25 years.³ X-rays can break the strands of DNA in cell nuclei. Toxins like benzo[a]pyrene⁴ , medications like those used in chemotherapy⁵ , and that most deadly poison, cigarette smoke, all cause DNA damage.