In genetic engineering, a vector is:

• A. A host cell
• B. A bacterial plasmid, virus, or other agent used to transfer genetic material
• C. A nutrient medium
• D. A gene sequence

Answer: (B)

A vector is the delivery vehicle that carries foreign DNA into a host cell so the gene of interest can be introduced and expressed. It is typically a DNA molecule such as a bacterial plasmid or a viral genome engineered to include the gene of interest and features that help propagate and select cells that receive it. This distinguishes it from a host cell, which is the system being transformed; a nutrient medium, which simply supports growth; and a gene sequence, which is the cargo being delivered rather than the carrier.