Which term describes a small, circular DNA molecule often used in genetic engineering?

• A. Chromosome
• B. Nucleus
• C. Genome
• D. Plasmid

Answer: (C)

When discussing a small circular DNA molecule used in genetic engineering, the term is plasmid. A plasmid is a separate, circular piece of DNA that can replicate independently of the main chromosomal DNA, and it’s commonly used as a cloning vector to carry foreign DNA into host cells. Plasmids often contain an origin of replication and a selectable marker, along with a region where scientists can insert genes of interest, making it easy to propagate and identify cells that have taken up the plasmid. In contrast, a chromosome is a much larger DNA structure that carries the essential genes of an organism, and the genome refers to the entire set of genetic material inside the organism. The nucleus is the cell compartment that houses chromosomes in many organisms. Therefore, the small circular DNA molecule used in genetic engineering is a plasmid.