uSnapback walks you through a few short steps to design a snapback primer for a single-base variant (SNV).

1. Amplicon sequence – Input the DNA sequence you want to amplify (A, C, G, T). Spaces, tabs, and new line breaks are OK.
2. Pick primers – Drag on the amplicon 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 some space between them.
3. Choose the SNV – Enter or click the SNV index, then choose the variant base. The SNV location cannot overlap a primer-binding site and must be a few bases away from both primers.
4. Target T_m – Enter the desired melting temperature for the wild-type snapback.

At the end, the results page shows the snapback primer and the limiting primer (with copy buttons), an extended snapback primer, and estimated 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.