Statement I: The foreign DNA and the vector DNA are cut with different restriction enzymes so that their sticky ends differ.
Statement II: DNA ligase acts on cut DNA molecules and joins their ends.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Only statement II is correct.
To make recombinant DNA, the foreign DNA and the vector are cut with a restriction enzyme. The cut pieces are then joined by DNA ligase.
Statement I: The foreign DNA and the vector DNA are cut with different restriction enzymes so that their sticky ends differ. — False. Both are cut with the same restriction enzyme. This gives the same kind of sticky ends, which pair with each other so that the two pieces can be joined. Different sticky ends would not pair.
Statement II: DNA ligase acts on cut DNA molecules and joins their ends. — True. DNA ligase seals the cut ends together. This is how the gene of interest is linked to the vector to make recombinant DNA.
NCERT Extract:
Restriction Enzymes – “… Restriction endonucleases are used in genetic engineering to form ‘recombinant’ molecules of DNA, which are composed of DNA from different sources/genomes. When cut by the same restriction enzyme, the resultant DNA fragments have the same kind of ‘sticky-ends’ and, these can be joined together (end-to-end) using DNA ligases (Figure 9.2).”
Principles of Biotechnology – “… The linking of antibiotic resistance gene with the plasmid vector became possible with the enzyme DNA ligase, which acts on cut DNA molecules and joins their ends.”