What features of plasmid ends allow them to join with foreign DNA?

• A. Complementary base pairing
• B. Sticky ends
• C. Unpaired bases
• D. DNA ligase

Answer: (B)

Sticky ends are single-stranded overhangs left when restriction enzymes cut DNA in a staggered way. These overhangs carry specific sequences that are complementary to the foreign DNA fragment being inserted, so they can pair up through base matching. That complementary pairing helps the foreign DNA align with the plasmid in the correct orientation. Once the ends are aligned, DNA ligase seals the gaps in the sugar-phosphate backbone to produce a continuous, recombinant plasmid. The key feature here is the overhangs that enable pairing; blunt ends lack those overhangs and don’t guide pairing as efficiently, and DNA ligase is the sealing step, not the feature of the ends themselves.