Arrange the following events in the order in which they took place:
A. Alfred Hershey and Martha Chase gave the unequivocal proof that DNA is the genetic material.
B. Friedrich Meischer identified DNA as an acidic substance present in the nucleus and named it ‘Nuclein’.
C. James Watson and Francis Crick proposed the Double Helix model for the structure of DNA.
D. Oswald Avery, Colin MacLeod and Maclyn McCarty worked to determine the biochemical nature of the ‘transforming principle’.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → B, D, A, C
B. Friedrich Meischer identified DNA as an acidic substance present in the nucleus and named it ‘Nuclein’. — First. This was in 1869, almost at the time of Mendel’s work. DNA was known as a substance long before anyone knew it carried genes.
D. Oswald Avery, Colin MacLeod and Maclyn McCarty worked to determine the biochemical nature of the ‘transforming principle’. — Second. Their work (1933-44) followed Griffith’s experiment of 1928 and showed that DNA caused transformation, though not all biologists were convinced.
A. Alfred Hershey and Martha Chase gave the unequivocal proof that DNA is the genetic material. — Third. Their bacteriophage experiment (1952) settled the protein versus DNA debate.
C. James Watson and Francis Crick proposed the Double Helix model for the structure of DNA. — Fourth. The model came in 1953, a year after the Hershey-Chase proof. It explained how the genetic material could be copied.
NCERT Extract:
Structure of Polynucleotide Chain – “DNA as an acidic substance present in nucleus was first identified by Friedrich Meischer in 1869. He named it as ‘Nuclein’. However, due to technical limitation in isolating such a long polymer intact, the elucidation of structure of DNA remained elusive for a very long period of time. It was only in 1953 that James Watson and Francis Crick, based on the X-ray diffraction data produced by Maurice Wilkins and Rosalind Franklin, proposed a very simple but famous Double Helix model for the structure of DNA.”
Biochemical Characterisation of Transforming Principle – “Prior to the work of Oswald Avery, Colin MacLeod and Maclyn McCarty (1933-44), the genetic material was thought to be a protein. They worked to determine the biochemical nature of ‘transforming principle’ in Griffith’s experiment.”
The Genetic Material is DNA – “The unequivocal proof that DNA is the genetic material came from the experiments of Alfred Hershey and Martha Chase (1952). They worked with viruses that infect bacteria called bacteriophages.”