Describe how the gene could have been removed from bacterial DNA.

• A. Restriction endonucleases cut donor DNA at specific base sequences
• B. DNA ligase alone removes the gene from bacterial DNA
• C. PCR is used to cleave the gene
• D. Restriction endonucleases cut donor DNA and plasmid with the same enzyme to generate compatible ends

Answer: (D)

The key idea is to create matching ends on both the gene-containing donor DNA fragment and the plasmid so they can be joined together. Restriction endonucleases cut DNA at specific sequences. If the same enzyme is used on both the donor fragment and the plasmid, you generate compatible ends (sticky or blunt) that can pair up and be sealed by DNA ligase. This allows the gene to be removed from the donor DNA and inserted into the plasmid vector in a controlled way, producing a recombinant plasmid carrying the gene of interest.

Why the other statements don’t fit: using DNA ligase alone can’t cut DNA, so it can’t remove the gene from the DNA to begin with. PCR is a copying technique and, by itself, doesn’t create the compatible ends or enable insertion into a plasmid vector for gene transfer in this context. Cutting only the donor DNA without also cutting the plasmid would not produce ends that can be ligated into the plasmid.