Which of the following is NOT a method to produce DNA fragments?

• A. Using restriction enzymes to cut out gene from DNA
• B. Conversion of mRNA to complementary DNA
• C. Using a gene machine
• D. DNA ligase

Answer: (D)

The main idea here is telling apart techniques that actually create pieces of DNA from those that copy, assemble, or repair DNA. Restriction enzymes cut DNA at specific sites, producing distinct DNA fragments, so they clearly generate fragments. Converting mRNA to complementary DNA creates a DNA copy of the mRNA sequence, which gives you DNA but not by breaking DNA into fragments. A gene machine synthesizes DNA sequences, effectively building new DNA pieces, which are fragments you can use. DNA ligase, on the other hand, isn’t about making fragments; it seals nicks and joins DNA fragments together to form longer molecules. So the tool that isn’t used to produce DNA fragments is DNA ligase.