Which definition best describes a transgene?

• A. The section of DNA that will be deleted in a cell
• B. A gene found in the genome of a large number of species
• C. The section of a DNA molecule coding for a specific protein
• D. The fragment of DNA introduced into the nucleus of a cell

Answer: (D)

A transgene is a piece of DNA that comes from outside the organism and is inserted into a recipient cell with the intention of being inherited and expressed. The defining point is that it is introduced into the host’s genome, typically into the nucleus, so it can be carried along and potentially produce a new trait or function. This is why the best description is a fragment of DNA introduced into the nucleus of a cell.

The other ideas aren’t correct because a section of DNA to be deleted describes a deletion, not a foreign insertion; a gene found across many species describes a widely distributed native gene, not an introduced sequence; and a DNA region coding for a protein describes a gene in general, not the act of introducing a foreign piece of DNA into another organism.