DNA as genetic material: Revisiting classic experiments through a simple, practical class

Abstract

In 1928, Frederick Griffith demonstrated a transmission process of genetic information by transforming Pneumococcus. In 1944, Avery et al. demonstrated that Griffith's transforming principle was DNA. We revisited these classic experiments in a practical class for undergraduate students. Both experiments were reproduced in simple, adapted forms. Griffith's experiment was reproduced by mixing heat-killed, ampicillin-resistant E. coli with live ampicillin-susceptible E. coli, followed by plating samples in the presence or absence of the antibiotic. Cells were also plated separately as controls. Avery's work was reproduced by treating a purified plasmid harboring the ampicillin resistance gene with DNase I. Treated and untreated plasmids were then used to transform E. coli cells, which were plated in culture media containing ampicillin. The students received a class guide for understanding and performing the experiments. The original articles by Griffith and Avery et al. were also provided, along with a list of questions to encourage a discussion on the experimental approach and results. The expected results were obtained and the students successfully revisited the classic experiments, which revealed that DNA is genetic material. The class was very well accepted, as indicated by students' evaluations. Thus, we presented a quick, inexpensive class involving important concepts, which can be easily reproduced in any laboratory with minor resources. © 2009 by The International Union of Biochemistry and Molecular Biology.