Genetic determinants have been shown to consist of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Enzymes are synthesized under the direction of nucleic acids, and enzymes, thus synthesized, are responsible for essentially all processes that occur in microorganisms. Experiments with. both bacteria (pneumococci) and viruses (radioisotope tests) have established roles of nucleic acids as determinants in microbial variations.