Nucleic acid melting analysis with saturation dyes

A PCR reaction mixture, comprising:

• a pair of oligonucleotide primers configured for amplifying at least a portion of a target nucleic acid to generate an amplicon;
• a thermostable polymerase;
• an unlabeled probe comprising a nucleic acid having a nucleic acid sequence completely complementary to at least a portion of a first allele of the target nucleic acid, the unlabeled probe being blocked at its 3′-end to prevent extension of the unlabeled probe during amplification, the unlabeled probe being operable to hybridize to the first allele so as to form a first duplex and to hybridize with at least one mismatch to a second allele of the target nucleic acid so as to form a second duplex, with at least one mismatch to a third allele of the target nucleic acid so as to form a third duplex, and with at least one mismatch to a fourth allele of the target nucleic acid so as to form a fourth duplex, such that the unlabeled probe is adapted to bind differentially to the first allele, the second allele, the third allele, and the fourth allele;
• and
• a dsDNA binding dye having a percent saturation of at least 90%, the dsDNA binding dye operable to bind to any of the first duplex, second duplex, third duplex, or fourth duplex that are present in the solution, the dsDNA binding dye being provided at a concentration suitable for distinguishing between the first duplex, second duplex, third duplex, and fourth duplex by melting curve analysis of a signal produced by the dsDNA binding dye during melting of first duplex, second duplex, third duplex, or fourth duplex without the dsDNA binding dye redistributing enough during melting to obscure lower temperature melting transitions, wherein at the concentration provided, the dsDNA binding dye does not significantly inhibit amplification of the target nucleic acid,
• wherein the unlabeled probe and the dsDNA binding dye are free in solution, the unlabeled probe and dsDNA binding dye being operable for detecting a double-stranded nucleic acid using the dsDNA binding dye without immobilizing the unlabeled probe or the amplicon, the double-stranded nucleic acid comprising a strand of the amplicon hybridized to the unlabeled probe.