THE MAJOR contribution to biological sciences in this century has been the cracking of the genetic code. The demonstration that the genetic message is dependent upon sequences of purine and pyrimidine bases has spawned a new biology which has captured the imagination of students and investigators throughout the scientific world. However, the demonstration of the simplicity of this coding system has very sobering implications for the improvement of man. Because the genetic message is an assembly of many small pieces, improvement or modification of genetic abnormality by planned rearrangement seems virtually impossible. Beadle,1 in his excellent article on the new genetics, points out that in any given organism mutations represent more or less random changes in an elaborate set of instructions that for generations has been selected for its appropriate message. An excellent analogy makes this clear: "The Gettysburg Address is a carefully constructed and highly successful message. A