Avery, McCarty and MacLeod’s Experiment

Estimated time: 4 minutes

Maharashtra State Board: Class 12

Key Points: Avery, McCarty and MacLeod’s Experiment

In 1944, Oswald T. Avery, Colin M. MacLeod, and Maclyn McCarty proved that DNA is the genetic material (transforming principle).
They used cell-free extracts of heat-killed S strain bacteria and mixed them with harmless R strain bacteria.
Only DNA was able to transform the R strain into the virulent S strain, showing its role in heredity.
Treatment with proteases and RNases did not stop transformation, proving that protein and RNA are not genetic material.
Treatment with DNase stopped transformation, confirming that DNA is responsible for it.
This experiment provided strong evidence that DNA is the hereditary material, though final confirmation came later from the Hershey and Chase experiment.