A change in the structure of a gene resulting in an altered gene product, that is a protein, is called mutation. Most mutations have harmful effects in an organism. But a few may result in changes which can make that organism better adapted to its environment. In that case, natural selection acts to increase the frequency of the advantageous trait leading to evolution.This change in the structure of a gene or the genetic material DNA may be just a single base obstruction or that involving a few or more bases. A segment of DNA may be deleted in a gene or addition of a few bases in a gene may result in mutation.
Mutation can be either spontaneous or induced. The former occur due to unknown mutagenic agents present in the environment. Induced mutations are produced at will by subjecting the genetic material to a variety of known mutagens like X-rays, UV rays or some chemicals. Mutations lead to several disorders in humans which are inheritable. There are over 3000 diseases that are due to defects in single genes. But agricultural scientists make use of mutation to develop new improved varieties.