DNA is a dynamic and adaptable molecule. As such, the nucleotide sequences found within it are subject to change as the result of a phenomenon called mutation. Depending on how a particular mutation modifies an organism's genetic makeup, it can prove harmless, helpful, or even hurtful. Sometimes, a mutation may even cause dramatic changes in the physiology of an affected organism. Of course, in order to better understand the varying effects of mutations, it is first necessary to understand what mutations are and how they occur.