Question

Describe Avery, McLeod and McCarty's experiment. State its significance.

Answer 1

In 1944, Oswald Avery, Colin MacLeod and Maclyn McCarty identified that the DNA causes bacterial transformation and not proteins. They identified the transforming principle in Griffith’s experiment. They isolated cell extract from the virulent S-strain and treated it with pancreatic deoxyribonuclease (DNase) and Protease separately. This cell extract was then mixed with the non-virulent R strain. This extract was incubated and injected in mice. It was observed that virulent S-strain developed in the cell extract treated with protease while virulent S-strain did not develop in the cell extract treated with DNase. This proved that DNA was responsible for the transformation in Griffith’s experiment. DNA is the hereditary material of bacteria.

Significance: This experiment indicated that transformation requires DNA and DNA is the genetic material that is transferred between cells. This was the first suggestion of the importance of DNA.