The code consists of combinations of four simple units, called bases, named adenine (A), thymine (T), cytosine (C) and guanine (G).

• 编码是由四种简单的单位排列组合而成，这四种单位称为碱基，分别是腺嘌呤（A）、胸腺嘧啶（T）、胞嘧啶（C）及鸟粪嘌呤（G）。