Which property of $DNA$ double helix led Watson and Crick to hypothesise semiconservative mode of $DNA$ replication? Explain.

Give scientific reasons : $DNA$ and not $RNA$ is the genetic material in majority of organisms.
 

Which of the following is not correct for molecule acting as genetic material ?

Give an account of Hershey and Chase experiment. What did it conclusively prove?If both $DNA$ and proteins contained phosphorus and sulphur do you think the result would have been the same ?

In some viruses, $RNA$ is present instead of $DNA$ indicating that