# NEET Botany Molecular Basis of Inheritance Questions Solved

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How did Hershey and Chase establish that DNA is transferred from virus to bacteria ?       (5 marks)

1. Hershey and Chase (1952) worked with viruses that infect bacteria called bacteriophages.

2. Bacteriophage attaches to the bacteria and create to enter its genetic material (DNA) into the

bacterial cell. Virus controls bacterial DNA and instructs to make its own replica i.e. virus

particles.

3. They wanted to discover whether it was protein or DNA from the viruses that entered the                 bacteria.

4. They grew some viruses on a medium containing radioactive phosphorus $\left({}^{32}\mathrm{P}\right)$ and some other

on a medium containing radioactive sulphur $\left({}^{\mathit{35}}S\right)$.

5. Radioactive sulphur was incorporated in the protein part of virus as sulphur in present in the

amino acids of proteins but not in DNA.

6. Radioactive phosphorus was incorporated in the DNA part of virus as phosphorus is present in

the DNA not in protein.

7. These two phage preparations were allowed to infect the bacterial cells separately.

8. Before lysis of bacteria both the cultures were gently agitated in a blender to separate the viral

coats from bacterial cells.

9. The culture was then centrifuged to separate viral particles from the bacterial cells.

10. The heavier bacteria settled down in the form of pellets. The supernatant contains lighter viral

coats which do not enter in the bacteria cells.

11. Bacteria which were infected with radioactive ${}^{35}\mathrm{S}$ virus, was detected in supernatant not in

bacterial cells.

12. Bacteria which were infected with radioactive ${}^{32}\mathrm{P}$ virus was detected in bacterial cells not in

supernatant.

13. This indicates protein did not enter the bacteria from viruses. DNA is therefore the genetic

material that is passed from virus to bacteria.

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