One of the most important breakthroughs in the history of genetics was the discovery that mutations can be induced (Muller, 1930; Stadler, 1932). The high frequency with which ionizing radiation and certain chemicals can cause genes to mutate made it possible to perform genetic studies that were not feasible when only spontaneous mutations were available. As a result, much of our understanding of genetics of higher organisms is based upon studies utilizing induced mutations for analyzing gene function. Alkylating agents, which yield predominantly point mutations, have been especially valuable, since the resulting altered and truncated protein products help to precisely map gene and protein function. Because of the high mutational density and the great utility of point mutations, traditional chemical mutagenesis methods have continued to be popular in phenotypic screens despite the development of other mutagenic tools such as transposon mobilization (Bingham et al., 1981).
