Short single stranded DNA molecules of specific base sequence, labeled either radioactively or immunologically, that are used to detect and identify the complementary base sequence in a gene or genome by hybridizing specifically to that gene or sequence.
To find the location of a gene along a stretch of DNA, scientists may construct a DNA probe. This consists of a strand of DNA that is complementary to a portion of the DNA in the gene being sought. The probe DNA can be labelled for easy detection, for example with radioactive atoms (emitting radiation) or with a fluorescent dye. The target DNA is first separated into two strands, then the probe DNA is added. It will bind to a strand at the point where it recognises a sequence of bases. It can then be detected either by its emitted radioactivity or by its fluorescence.
Gene amplification & PCR glossary