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.
Pieces of the instructions on the genes can get knocked out or changed. When this occurs during the process of cell division, when the DNA is being copied to the new cell, a mutation occurs. If the mutation occurs in the wrong place -- in an active gene, for instance -- it can result in one of two things. It can disrupt the function of the cell, causing it to die. Or it can cause the cell to begin dividing wildly and become a cancer.