SNP genotyping by unlabeled probe melting analysis.

Fluorescent nucleic acid detection in polymerase chain reaction (PCR) generally uses oligonucleotide probes labeled with covalently attached dyes. However, unlabeled oligonucleotides in the presence of saturating DNA dyes can also serve as hybridization probes. The DNA dye, LCGreen Plus, and a 3'-blocked unlabeled probe are added before amplification, and asymmetric PCR is performed at a 1:5 to 1:10 primer ratio. After PCR is complete, fluorescent melting curves reveal both probe melting at low temperature and amplicon melting at high temperature. After background removal, the melting temperature(s) of the probe/target duplex specific to the allele(s) amplified are revealed. Probes between 20 and 40 bp with T(m)s between 50 and 85 degrees C are effective. The method requires only three standard oligonucleotides and endpoint fluorescence melting. No real-time PCR or allele-specific amplification is needed. Unlabeled probes are inexpensive, provide the sequence specificity of probes, and allow simultaneous identification of multiple alleles by melting analysis.