Correct Response: D. A virus is a partial string of DNA that is sometimes encapsulated within a protein shell. Viruses enter a cell and go to the cell's nucleus where they use the cell's reproductive mechanisms to make copies of themselves. Genetic engineers create special viruses that do not replicate themselves. Instead, these special viruses add their own DNA to that of the host cell and act as a vector for gene transfer. Insects (A) are often vectors of disease, but are not generally used in genetic engineering. Fungi (B) are not used for this purpose, and bacteria (C) are not commonly used as vectors in genetic engineering.
