附上IUPAC DNA字母表：
| Symbol | Bases | Origin of designation |
|---|---|---|
| G | G | 鸟嘌呤 |
| A | A | 腺嘌呤 |
| T | T | 胸腺嘧啶 |
| C | C | 胞嘧啶 |
| R | G or A | 嘌呤 |
| Y | T or C | 嘧啶 |
| M | A or C | 氨基 |
| K | G or T | 酮 |
| S | G or C | 强相互作用 (3 H bonds) |
| W | A or T | 弱相互作用 (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 |
| V | G or C or A | not-T (not-U), V follows U |
| D | G or A or T | not-C, D follows C |
| N | G or A or T or C | aNy |