How is the sea of electrons model is used to explain the physical properties of metals? electrons give off a charge, the greater or lesser the metal will depend on how packed the universe is in the metal, atoms and such.
Mutations can also be caused by exposure to specific chemicals or radiation. These agents cause the DNA to break down. This is not necessarily unnatural  even in the most isolated and pristine environments, DNA breaks down. Nevertheless, when the cell repairs the DNA, it might not do a perfect job of the repair.
A mutation is a change in a DNA sequence that alters the protein for which the DNA codes. Sometimes mutations occur due to damage from an outside source, such as ultraviolet radiation. Excess ultraviolet radiation from the sun sometimes causes mutations that lead a cell to become cancerous. Most mutations that damage a DNA strand are harmful. Other mutations occur due to deletion or insertion of DNA base pairs. One such deletion in humans confers HIV resistance or a delayed AIDS onset. Humans who are heterozygous for the mutation, meaning they possess one mutant gene and one normal gene, experience a slower progression of AIDS.