[pezzana]

> Crick and Watson certainly didn't discover DNA as the substrate for Mendelian inheritance, that was known long before. They (in collaboration with Rosalind "don't talk to me about this woman" Franklin) discovered its 3D structure.

From Wikipedia, it goes back to at least 1927:

... In 1927, Nikolai Koltsov proposed that inherited traits would be inherited via a "giant hereditary molecule" made up of "two mirror strands that would replicate in a semi-conservative fashion using each strand as a template".[186][187] In 1928, Frederick Griffith in his experiment discovered that traits of the "smooth" form of Pneumococcus could be transferred to the "rough" form of the same bacteria by mixing killed "smooth" bacteria with the live "rough" form.[188][189] This system provided the first clear suggestion that DNA carries genetic information.

https://en.wikipedia.org/wiki/DNA#History