What results from the experiments of Frederick Griffith provided the strongest support for his conclusion that a transformation factor is responsible for heredity?

Frederick Griffith conducted experiments in 1928 using two strains of Streptococcus pneumoniae: a virulent strain with a smooth appearance and a non-virulent strain with a rough appearance. He discovered that when he injected mice with heat-killed virulent bacteria mixed with live non-virulent bacteria, the mice developed pneumonia and died. This indicated that some 'transforming principle' from the dead bacteria was taken up by the live bacteria, transforming them into a virulent form.

Transformation is a process in which a bacterium takes up foreign DNA from its environment and incorporates it into its own genome. In Griffith's experiment, the non-virulent bacteria acquired the genetic material from the heat-killed virulent bacteria, leading to a change in phenotype. This concept is fundamental in genetics as it demonstrates how genetic information can be transferred between organisms, influencing traits and characteristics.

Building on Griffith's findings, the Avery-MacLeod-McCarty experiment in 1944 identified DNA as the 'transforming factor.' By treating the heat-killed virulent bacteria with enzymes that destroyed proteins, RNA, or DNA, they showed that only the destruction of DNA prevented transformation in the non-virulent bacteria. This provided strong evidence that DNA is the molecule responsible for heredity, supporting Griffith's initial conclusions about the transformation factor.