| 代码 | 英文含义 | 中文含义 | |
| G | Guanine | 鸟嘌啉 | |
| A | Adenine | 腺嘌啉 | |
| T | (U) | Thymine (Uracil) | 胸腺嘧啶 (尿嘧啶) |
| C | Cytosine | 胞嘧啶 | |
| R | (A or G) | PuRine | 嘌啉 |
| Y | (C or T or U) | Pyrimidine | 嘧啶 |
| M | (A or C) | Amino | 腺嘌啉或胞嘧啶(氨基) |
| K | (G or T) | Ketone | 鸟嘌啉或胸腺嘧啶(酮基) |
| S | (C or G) | Strong interaction | 强相互作用碱基 |
| W | (A or T) | Weak interaction | 弱相互作用碱基 |
| H | (A or C or T) | Not-G (H after G) | 非鸟嘌啉 |
| B | (C or G or T) | Not-A (B after A) | 非腺嘌啉 |
| V | (A or C or G) | Not-T/U (V after U) | 非胸腺嘧啶 |
| D | (A or G or T) | Not-C (D after C) | 非胞嘧啶 |
| N | (A or C or G or T) | Any | 不确定 |