In its earliest manifestations, molecular biology&mdash;the name was coined by Warren Weaver of the Rockefeller Foundation in 1938&mdash;was an idea of physical and chemical explanations of life, rather than a coherent discipline.  Following the advent of the Mendelian-chromosome theory of heredity in the 1910s and the maturation of atomic theory and quantum mechanics in the 1920s, such explanations seemed within reach.  Weaver and others encouraged (and funded) research at the intersection of biology, chemistry and physics, while prominent physicists such as Niels Bohr and Erwin Schrödinger turned their attention to biological speculation.  However, in the 1930s and 1940s it was by no means clear which&mdash;if any&mdash;cross-disciplinary research would bear fruit; work in colloid chemistry, biophysics and radiation biology, crystallography, and other emerging fields all seemed promising.
In 1940, George Beadle and Edward Tatum demonstrated the existence of a precise relationship between genes and proteins. In the course of their experiments connecting genetics with biochemistry, they switched from the genetics mainstay Drosophila to a more appropriate model organism, the fungus Neurospora; the construction and exploitation of new model organisms would become a recurring theme in the development of molecular biology.  In 1944, Oswald Avery, working at the Rockefeller Institute of New York, demonstrated that genes are made up of DNA (see Avery–MacLeod–McCarty experiment). In 1952, Alfred Hershey and Martha Chase confirmed that the genetic material of the bacteriophage, the virus which infects bacteria, is made up of DNA (see Hershey–Chase experiment). In 1953, James Watson and Francis Crick discovered the double helical structure of the DNA molecule based on the discoveries made by Rosalind Franklin. In 1961, François Jacob and Jacques Monod demonstrated that the products of certain genes regulated the expression of other genes by acting upon specific sites at the edge of those genes.  They also hypothesized the existence of an intermediary between DNA and its protein products, which they called messenger RNA. Between 1961 and 1965, the relationship between the information contained in DNA and the structure of proteins was determined: there is a code, the genetic code, which creates a correspondence between the succession of nucleotides in the DNA sequence and a series of amino acids in proteins.
In April 2023, scientists, based on new evidence, concluded that Rosalind Franklin was a contributor and "equal player" in the discovery process of DNA, rather than otherwise, as may have been presented subsequently after the time of the discovery.
The chief discoveries of molecular biology took place in a period of only about twenty-five years. Another fifteen years were required before new and more sophisticated technologies, united today under the name of genetic engineering, would permit the isolation and characterization of genes, in particular those of highly complex organisms.