What feature allows DNA fragments to join to plasmids cut with the same restriction enzyme?

• A. Sticky ends
• B. Blunt ends
• C. Random ends
• D. No ends

Answer: (A)

Joining DNA fragments cut by the same restriction enzyme relies on sticky ends: short single-stranded overhangs created when the enzyme makes staggered cuts. These overhangs are complementary between the plasmid and the insert, so they can base-pair with each other, correctly aligning the pieces for ligation by DNA ligase. This base-pairing guidance makes the process efficient and directional, which is why sticky ends are favored for cloning with the same enzyme. Blunt ends have no overhangs and lack this complementary pairing, making the joining less efficient and more random.