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 the base sequence of DNA that can affect the structure and function of proteins when they occur within a gene. Mutations can be spontaneously caused by copying errors during DNA replication or induced by exposure to external elements such as chemical mutagens, radiation or viruses. Cystic fibrosis is an example of a disease which can result from a nonsense mutation (this may not be the only cause though). 2  Frameshift mutations occur when the addition or removal of a base alters the reading frame of the gene.