Final answer:
Frederick Griffith first identified transformation, but it was Avery, MacLeod, and McCarty who concluded that DNA is the genetic material.
Step-by-step explanation:
Discovery of DNA as Genetic Material
The identification of DNA as the genetic material responsible for transformation was first carried out by Frederick Griffith. In 1928, Griffith's experiment with Streptococcus pneumoniae led to the discovery of the phenomenon known as transformation, where genetic information could be transferred from one cell to another. However, it was Avery and his colleagues who, in the 1940s, identified DNA as the molecule responsible for this process. Avery, MacLeod, and McCarty performed experiments that clearly proved DNA, not proteins or other cellular components, was the "stuff of genes". They did this by inactivating the DNA in the S strain of bacteria and observing that when DNA was inactivated, the R-strain bacteria could not be transformed to become virulent.