Methods for detecting nucleic acid sequence variants

1. A method for detecting the presence or absence of a nucleic acid variant in a target region comprising

amplifying the target region with a forward primer and a reverse primer in the presence of a selector blocker, wherein the selector blocker comprises a sequence complementary to the target region except at a location where the nucleic acid variant occurs,

wherein the selector blocker is configured as a switch-blocker and wherein the switch-blocker comprises a 5′ switch sequence linked or conjugated to a 3′ long hybridizing region, wherein the 3′ long hybridizing region is complementary to and binds a region adjacent to or near the target region, and wherein (i) the 5′ switch sequence is capable of binding tightly to the target region such that the bound switch sequence functions as a steric blocker preventing extension of the forward primer, or (ii) the 5′ switch sequence is not capable of binding tightly to the target region such that the switch sequence is partially open and the forward primer can extend; and

wherein amplification of the target region is indicative of the presence of the nucleic acid variant in the target region and wherein the absence of amplification is indicative of the absence of the nucleic acid variant in the target region.

2. The method of claim 1 , wherein the nucleic acid variant includes a deletion, mutation, or insertion.

3. The method of claim 1 , wherein the selector blocker is non-extendable.

4. The method of claim 1 , wherein the switch sequence is linked to the long hybridizing region via a bridging linkage.

5. The method of claim 4 , wherein the bridging linkage comprises a nucleotide sequence.

6. The method of claim 4 , wherein the bridging linkage comprises a non-nucleotide linkage.

7. The method of claim 4 , wherein the bridging linkage comprises both nucleotide and non-nucleotide linkages.

8. The method of claim 1 , wherein the selector blocker is protected against 3′ or 5′ exonuclease activity.

9. The method of claim 1 , wherein the affinity of the selector blocker for a target sequence in the target region is increased.

10. The method of claim 1 , wherein the selector blocker does not contain PNA or LNA.

11. The method of claim 1 , wherein the selector blocker comprises a detectable entity.

12. The method of claim 11 , wherein the selector blocker comprises a fluorescent label and a quencher.

13. The method of claim 1 , wherein the 3′ end of the forward primer when hybridized to the target region is located less than about 30 nucleotides away from the nucleic acid variant in the target region.

14. The method of claim 1 , wherein the 3′ end of the forward primer hybridizing to the target region overlaps with the 5′ end of the switch sequence of the selector blocker hybridizing to the target region.

15. The method of claim 14 , wherein the 5′ end of the switch sequence of the selector blocker does not contain the nucleic acid variant.

16. The method of claim 1 further comprising detecting amplification of the target region via obtaining a melting curve or sequencing of the amplified product.

17. The method of claim 1 further comprising detecting amplification of the target region via comparing the quantity of the amplified product to a predetermined level associated with presence or absence of the nucleic acid variant in the target region.

18. The method of claim 1 , wherein the amplification is by digital PCR.

19. The method of claim 1 , wherein the forward primer does not overlap with the switch sequence.

20. The method of claim 1 , wherein the 3′ long hybridizing region has a higher Tm than the switch sequence.

21. The method of claim 1 , wherein the 3′ end of the forward primer is complementary to a sequence located more than 0 nucleotides away from the nucleic acid variant and the 3′ end of the reverse primer is complementary to a sequence located more than 0 nucleotides away from the nucleic acid variant.

22. The method of claim 1 , wherein the amplification is performed in the presence of an enzyme possessing 3′ exonuclease repair activity.

23. The method of claim 1 , wherein the 5′ switch sequence is non-covalently linked to the 3′ long hybridizing region.

24. The method of claim 1 , where the selector blocker and forward primer are linked or conjugated to each other.

25. The method of claim 24 , wherein the selector blocker and forward primer are non-covalently linked.

26. A method for detecting the presence or absence of a nucleic acid variant in a target region comprising amplifying the target region with a forward primer and a reverse primer in the presence of a selector blocker, wherein the selector blocker comprises a sequence complementary to the target region in the presence of the nucleic acid variant,

wherein the selector blocker is configured as a switch-blocker and wherein the switch-blocker comprises a 5′ switch sequence linked or conjugated to a 3′ long hybridizing region, wherein the 3′ long hybridizing region is complementary to and binds a region adjacent to or near the target region, and wherein (i) the 5′ switch sequence is capable of binding tightly to the target region such that the bound switch sequence functions as a steric blocker preventing extension of the forward primer, or (ii) the 5′ switch sequence is not capable of binding tightly to the target region such that the switch sequence is partially open and the forward primer can extend;

wherein amplification of the target region is indicative of the presence of at least one non-variant nucleotide in the target region and wherein the absence of amplification is indicative of the absence of non-variant nucleotides in the target region.

27. The method of claim 26 , wherein the switch sequence is linked to the long hybridizing region via a bridging linkage.

28. The method of claim 27 , wherein the bridging linkage comprises a nucleotide sequence.

29. The method of claim 27 , wherein the bridging linkage comprises a non-nucleotide linkage.

30. The method of claim 27 , wherein the bridging linkage comprises both nucleotide and non-nucleotide linkages.