A system for selectively detecting a target nucleotide sequence, said system comprising at least one probe:antiprobe system comprising; (a) a probe oligonucleotide comprising a nucleotide sequence complementary to a first target nucleotide sequence, and a first label moiety attached thereto; and (b) an antiprobe oligonucleotide comprising a nucleotide sequence fully complementary to the probe oligonucleotide except for at least one mismatched base in a non-terminal position, and a second label moiety, wherein the second label moiety is attached to the antiprobe oligonucleotide or is a region of the antiprobe oligonucleotide, wherein: (i) the probe oligonucleotide is configured for greater hybridization affinity for the first target nucleotide sequence than for the antiprobe oligonucleotide; and the antiprobe oligonucleotide is configured for greater hybridization affinity for the probe oligonucleotide than the probe oligonucleotide has hybridization affinity for a second target nucleotide sequence of interest; (ii) in the presence of the first target nucleotide sequence, the probe oligonucleotide and the first target nucleotide sequence form a duplex, whereupon the first and the second label moieties do not interact, thereby providing a first detectable signal; (iii) in the absence of the first target nucleotide sequence, the probe oligonucleotide and the antiprobe oligonucleotide form a duplex, thereby allowing the first and the second label moieties to interact to provide a modulated detectable signal, wherein the first and the modulated detectable signals are distinguishable; and (iv) in the presence of the second target nucleotide sequence differing from the first target sequence by at least one base mismatch, the probe oligonucleotide and the antiprobe oligonucleotide preferentially form a duplex, thereby inhibiting the probe oligonucleotide from forming a duplex with the second target nucleotide sequence. (a) a probe oligonucleotide comprising a nucleotide sequence complementary to a first target nucleotide sequence, and a first label moiety attached thereto; and (b) an antiprobe oligonucleotide comprising a nucleotide sequence fully complementary to the probe oligonucleotide except for at least one mismatched base in a non-terminal position, and a second label moiety, wherein the second label moiety is attached to the antiprobe oligonucleotide or is a region of the antiprobe oligonucleotide, wherein: (i) the probe oligonucleotide is configured for greater hybridization affinity for the first target nucleotide sequence than for the antiprobe oligonucleotide; and the antiprobe oligonucleotide is configured for greater hybridization affinity for the probe oligonucleotide than the probe oligonucleotide has hybridization affinity for a second target nucleotide sequence of interest; (ii) in the presence of the first target nucleotide sequence, the probe oligonucleotide and the first target nucleotide sequence form a duplex, whereupon the first and the second label moieties do not interact, thereby providing a first detectable signal; (iii) in the absence of the first target nucleotide sequence, the probe oligonucleotide and the antiprobe oligonucleotide form a duplex, thereby allowing the first and the second label moieties to interact to provide a modulated detectable signal, wherein the first and the modulated detectable signals are distinguishable; and (iv) in the presence of the second target nucleotide sequence differing from the first target sequence by at least one base mismatch, the probe oligonucleotide and the antiprobe oligonucleotide preferentially form a duplex, thereby inhibiting the probe oligonucleotide from forming a duplex with the second target nucleotide sequence. (i) the probe oligonucleotide is configured for greater hybridization affinity for the first target nucleotide sequence than for the antiprobe oligonucleotide; and the antiprobe oligonucleotide is configured for greater hybridization affinity for the probe oligonucleotide than the probe oligonucleotide has hybridization affinity for a second target nucleotide sequence of interest; (ii) in the presence of the first target nucleotide sequence, the probe oligonucleotide and the first target nucleotide sequence form a duplex, whereupon the first and the second label moieties do not interact, thereby providing a first detectable signal; (iii) in the absence of the first target nucleotide sequence, the probe oligonucleotide and the antiprobe oligonucleotide form a duplex, thereby allowing the first and the second label moieties to interact to provide a modulated detectable signal, wherein the first and the modulated detectable signals are distinguishable; and (iv) in the presence of the second target nucleotide sequence differing from the first target sequence by at least one base mismatch, the probe oligonucleotide and the antiprobe oligonucleotide preferentially form a duplex, thereby inhibiting the probe oligonucleotide from forming a duplex with the second target nucleotide sequence.