[50 years of molecular biology].

In 1865, Johann Gregor Mendel laid the mathematical foundation of the science of genetics. His "elements of heredity" (later called genes) were postulated as pure algebraic units. At about the same time (1868), Friedrich Miescher extracted a gelationous substance from the nuclei of white blood cells found in pus. This substance was called nuclein; later it became known as nucleic acid. Fifty years ago, Oswald T. Avery and his colleagues showed that one type of nucleic acid--DNA mediates genetic transformation in pneumococci. This was the first demonstration that Miescher's nuclein is the repository of Mendel's hypothetical elements of heredity. The genes thus "materialized". Although not recognized by contemporaries, Avery's discovery may be considered as a landmark in the history of biology. The molecular era of genetics and biology has begun. Other events associated with the beginning of this new era (bacteriophage research, work on nutritional mutants in Neurospora) are also described in the present review.