| Sequence Utility by Ivano Zara Riccardo Schiavon |
| IUPAC Code | ||
| Symbol Meaning Origin of designation | ||
| G | G | Guanine |
| A | A | Adenine |
| T | T | Thymine |
| C | C | Cytosine |
| R | G or A | puRine |
| Y | T or C | pYrimidine |
| M | A or C | aMino |
| K | G or T | Keto |
| S | G or C | Strong interaction (3 H bonds) |
| W | A or T | Weak interaction (2 H bonds) |
| H | A or C or T not-G | H follows G in the alphabet |
| B | G or T or C not-A | B follows A in the alphabet |
| V | G or C or A not-T (not-U) | V follows U in the alphabet |
| D | G or A or T not-C | D follows C in the alphabet |
| N | G or A or T or C | aNy |