All of the following describe a nucleic acid probe except:

• A. Short strand of DNA of a known sequence
• B. Short strand of RNA of a known sequence
• C. Can be cloned in bacteria
• D. Can be labeled with avidin

Answer: (D)

A nucleic acid probe is a short strand of DNA or RNA with a known sequence that can bind specifically to a complementary target sequence. These probes are often produced by cloning the desired sequence in bacteria, enabling amplification and bulk production. They are typically labeled with detectable tags such as biotin, fluorescent dyes, or digoxigenin, which allow visualization when the probe hybridizes to its target. If biotin is used, detection relies on avidin or streptavidin binding to the biotin label, but the probe itself is not labeled with avidin. That makes the statement about labeling with avidin incorrect, while the others correctly describe features of nucleic acid probes.