DNA probes can be defined as fragments of single stranded DNA molecules, which are used to to detect the presence of target DNA sample. The nucleotide sequence in probes is complementary to the nucleotide sequence of target DNA.
Hence, probes detect DNA by hybridizing to single stranded target DNA according to complementary base-pairing rule. Nitrogen bases present in probe and target DNA make hydrogen bonds with each other (adenine binds with thymine and guanine binds with cytosine (and vice versa) and target DNA is detected.
Thus, the correct answer is 'complementary base-pairing.'
