Final answer:
DNA ligase is required in a test tube to create recombinant DNA with long-term stability by repairing the phosphodiester backbone and forming stable bonds.
Step-by-step explanation:
To create recombinant DNA with long-term stability, it is necessary to have DNA ligase in the test tube.
The purpose of DNA ligase is to repair the phosphodiester backbone of DNA, specifically after the foreign DNA has been inserted into a plasmid vector with the help of restriction enzymes.
During the recombination process, the restriction enzyme creates complementary sticky ends on the foreign DNA fragment and the plasmid, allowing them to anneal.
DNA ligase then facilitates the formation of stable phosphodiester bonds, ensuring that the recombinant plasmids are sealed and stable.