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.
Updated August 03, 2017. DNA mutations happen when there are changes in the nucleotide sequence that makes up the strand of DNA. This can be caused by random mistakes in DNA replication or even an environmental influence like UV rays or chemicals.