Describe Hershey - Chase experiment or How it was proved the DNA is genetic material ?
 

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.

$\Rightarrow$ The bacteriophage attaches to the bacteria and its genetic material then enters the bacterial cell.

The bacterial cell treats the viral genetic material as if it was its own and subsequently manufactures more virus particles.

Hershey and chase worked to discover whether it was protein or $DNA$ from the viruses that entered the bacteria.

They grew some viruses on a medium that contained radioactive phosphorus and some others on medium that contained radioactive sulfur.

Viruses grow in the presence of radioactive phosphorous contained radioactive $DNA $ but not radioactive protein because $DNA$ contains phosphorus but protein does not.

Similarly viruses grown on radioactive sulfur contained radioactive protein but not radioactive $DNA$ because $DNA$ does not contain sulfur.

Radioactive phages were allowed to attach to E. coli bacteria.

Then, as the infection proceeded, the viral coats were removed from the bacteria by agitating them in a blender.

The virus particles were separated from the bacteria by spinning them in a centrifuge.

Bacteria which was infected with viruses that had radioactive $DNA$ were radioactive, indicating that $DNA$ was the material that passed from the virus to the bacteria.

Bacteria that were infected with viruses that had radioactive proteins were not radioactive. This indicates that proteins did not enter the bacteria from the viruses.