Question: 116 Unequivocal proof that DNA is the genetic material was first proposed by
(1) Avery, Macleoid and McCarthy
(2) Wilkins and Franklin
(3) Frederick Griffith
(4) Alfred Hershey and Martha Chase
Answer: Option (4)
Explanation:
Frederick Griffith performed the transformation experiment in 1928, which showed that some “transforming principle” was transferred from dead bacteria to living bacteria,
but he could not identify the nature of this genetic material.
Avery, MacLeod and McCarty later demonstrated that DNA was responsible for transformation,
but their results were not universally accepted as final proof.
The unequivocal proof that DNA is the genetic material was provided by
Alfred Hershey and Martha Chase in 1952 using bacteriophages.
In their experiment, DNA of bacteriophage was labelled with radioactive phosphorus ^{32}P, while the protein coat was labelled with radioactive sulfur ^{35}S.
After infection of bacteria and subsequent blending and centrifugation, it was observed that only
^{32}P-labelled DNA entered the bacterial cells,
whereas ^{35}S-labelled protein remained outside.
This conclusively proved that DNA, and not protein, is the genetic material,
making Option (4) the correct answer.