Chapter 3 - Avery, MacLeod, and McCarty Identified DNA as the Genetic Material: A Celebrated Case of a Clinical Observation That Led to a Fundamental Basic Discovery

Abstract

This chapter describes the 1944 groundbreaking discovery by Oswald Avery, Colin MacLeod, and Maclyn McCarty that DNA is the genetic material that dictates phenotypic traits in the pathogenic bacterium pneumococcus. Considered today to be the harbinger of molecular biology, this identification of DNA as the hereditary material defied the commonly held belief of the time that genes were made of proteins. Peculiarly, this landmark discovery was somewhat inadvertent since Avery’s initial objective had not been to identify the chemical basis of inheritance. Rather, he was a bacteriologist whose life work was dedicated to the immunochemistry of pneumococcus with the intention of developing an effective vaccine against this pathogen. This chapter describes the historical background and the scientific circumstances of Avery’s research, from clinically oriented studies of pneumococcus to its ultimate culmination in the unanticipated milestone finding that DNA is the genetic material.