Snapback primers enable genotyping with 2 unlabeled primers and a dsDNA dye. No fluorescent labels or probes are necessary. A 5'-tail is added to one of the primers that hybridizes to the variant site.

uSnapback designs a snapback primer for genotyping of a single-base variant (SNV).

1. Enter sequence – Input or copy/paste the DNA sequence containing the amplicon you want to amplify (A, C, G, T). Spaces, tabs, and new line breaks are OK.
2. Pick primers – Drag on the sequence to select the forward primer, then drag to select the reverse primer. The reverse primer must be to the right of the forward primer, and there must be at least 7 bases between them.
3. Choose the SNV – Click on the SNV, then choose the variant base. The SNV location cannot overlap a primer-binding site and must be at least 3 bases away from both primers.
4. Target T_m – Enter the desired melting temperature for the wild-type snapback.

The results page will show the snapback primer and the limiting primer sequences (with copy buttons), the secondary structure of the extended snapback primer, and the predicted wild-type and variant T_m values.

If you need to change something, use Back to keep your inputs, or Restart to clear everything and start over.