Q. 9.  Replication was allowed to take place in the presence of radioactive deoxynucleotides precursors in E.coil that was a mutant for DNA ligase. Newly synthesised radioactive DNA was purified strands were separate by denaturation. These were centrifuged using density gradient centrifugation. Which of the following would be a correct result?

 

In above case, as E.coli is a mutant for DNA  ligase, it will result in no further joining of Okazaki fragments on lagging strand.

This will ultimately result in the formation of both high molecular weight fragments (on leading strands) and low molecular weight fragments (on lagging strand). Hence, only the graph (a) could be the appropriate result after centrifugation.