Question

In 1928, the bacteriologist Frederick Griffith conducted transformation experiments. How did these experiments contribute to the history of molecular genetics?

Answer 1

In 1928, Frederick Griffith showed that a heritable “transforming principle” could move between strains of Streptococcus (Diplococcus) pneumoniae: live non‑virulent rough (R) cells mixed with heat‑killed virulent smooth (S) cells produced disease in mice and yielded live S‑type bacteria, demonstrating that some chemical factor from the dead S cells permanently converted R cells to the virulent form. Although Griffith did not identify the chemical nature of that factor, his result was the first clear experimental demonstration that an external molecule can carry and transfer inherited traits, which converted the question of inheritance into a tractable biochemical problem and directly motivated Avery, MacLeod and McCarty’s 1944 work that identified DNA as the transforming substance; together with later experiments (e.g., Hershey–Chase) and the discovery of DNA’s structure, Griffith’s finding set the experimental path that established DNA as the genetic material and launched modern molecular genetics.