Which vector feature can distinguish recombinant and non-recombinant colonies?

Correct answer: Screening marker

The direct answer is option A: a screening marker. A vector feature used in screening helps a researcher distinguish colonies that contain a recombinant construct from colonies that do not. For example, in lacZ-based blue-white screening, insertion of foreign DNA can disrupt lacZ activity. Under the proper indicator conditions, colonies with an intact lacZ region may appear blue, whereas colonies with the inserted fragment may appear white. The exact color result depends on the host and medium, but the principle is differential identification. Option A is correct because a screening marker gives a visible or testable difference between colony types. Option B is wrong because ori, the origin of replication, helps the vector replicate; it does not by itself distinguish recombinant from non-recombinant colonies. Option C is wrong because the host cell wall is not a vector screening feature. Option D is wrong because a water molecule has no role in identifying recombinant colonies. Do not confuse a selectable marker with a screening marker: selection allows certain cells to grow, while screening helps distinguish among survivors. Memory cue: selection answers “who grows?”; screening answers “which survivor is recombinant?”