ABSTRACT
In 1927, H.J. Muller first demonstrated that X-irradiation of the sperm of the fruit fly, Drosophila melanogaster, induces gene mutation. Radiation is one of the many environmental agents that cause genetic defects. In addition, many spontaneous mutations may result from errors made during the replication of genetic materials. Almost all mutations are harmful to a varying degree for the organisms; however, mutations have been the basis for evolution of animal species.
