Mutation is an abrupt change in the genotype of an organism, not resulting from genetic recombination. There are three main types of mutational change. In the first type the genetic material is altered quantitatively, either by the addition or removal of whole chromosomes, parts of chromosomes, or whole chromosome sets; or, at the other extreme, by the addition or deletion of single base pairs from the nucleic acid of the gene. The second type are qualitative alterations of the genetic material, such as the substitution of one base pair for another. In the third type the existing genetic material may be rearranged without altering its quantity or quality. Because of the genetic complexity of man, there are immense possibilities for mutation. Genetic diseases are becoming relatively more important owing to the reduction in the incidence and severity of parasitic and bacterial diseases.
Two main types of genetic damage are recognized: chromosome aberrations and gene mutations. These may affect either somatic cells or germinal cells. Although damage to either cell population may have serious consequences, from the public health standpoint mutations in germinal cells are of paramount importance, as they present a hazard to future generations. The relation between the ability of a chemical to produce mutations in experimental test systems and its ability to affect humans is not firmly established but the potential hazard to the population is of great magnitude.
It is a problem for the human race that bacterial viruses can mutate, for it means that antibiotics are effective for only a limited time, until the virus has mutated to survive the drug treamennt.
If there were no mutations there would be no genetic differences among organisms and no evolution of life. In fact, mutations have often been called the building blocks of evolution. For this reason, the mutation process is fundamental not only to genetics but to the continuation of life itself in a world that is changing.
