What is a gene probe?

• A. Strand of DNA; short up to 20 bases long; complementary to part of target gene; with radioactive labeling / fluorescent labeling
• B. A protein that binds to DNA
• C. A long RNA sequence used for silencing
• D. A plasmid used to deliver a gene

Answer: (A)

A gene probe is a short, labeled single-stranded DNA fragment that is designed to be complementary to a specific part of the target gene. Because it pairs with the exact sequence of interest, it can hybridize to the target in a sample, allowing detection. The labeling—radioactive or fluorescent—provides a signal so you can see where the probe has bound, helping identify whether the gene is present and where it is located. This concept hinges on specific base pairing and labeled detection to reveal the target sequence. Other descriptions refer to different tools: a DNA-binding protein is not a probe, a long RNA sequence used for silencing is an RNA interference molecule, and a plasmid used to deliver a gene is a gene delivery vector.