Which option shows a correct use of ligase?

Correct answer: Joining insert DNA with a plasmid vector

DNA ligase joins an insert DNA fragment to a plasmid vector by forming phosphodiester bonds between DNA fragments. Therefore, it is used to make recombinant DNA during gene cloning. Cutting DNA at specific sites is done by restriction enzymes, not ligase. Exam tip: remember that restriction enzymes cut DNA, whereas ligase joins DNA fragments.