| Symbol | Description |
|---|---|
| A | Adenine |
| C | Cytosine |
| G | Guanine |
| T | Thymine |
| U | Uracil |
| R | Purine A or G |
| Y | Pyrimidine C or T (U) |
| M | Amino A or C |
| K | Keto G or T (U) |
| S | C or G strong (3 H bonds) |
| W | A or T (U) weak (2 H bonds) |
| B | Not A |
| D | Not C |
| H | Not G |
| V | Not T (U) |
| N | Any nucleotid |