测序是指描述DNA或蛋白质中重复单位的序列。DNA和蛋白质都是由包含重复单位的链组成。对DNA来说，这些单位是C、T、A和G碱基，对蛋白质来说这些单位是20个不同的氨基酸。这些重复单位的序列是其所携带信息的重要部分。组成DNA的碱基序列构成合成蛋白质的密码，而蛋白质中氨基酸的排列决定了蛋白质的结构和功能。在用测序仪对DNA测序前要对其进行复制和荧光标记。蛋白质自动测序系统从蛋白质一端每次切下一个氨基酸残基并识别。

Sequencing refers to the delineation of the order of the repeating units in DNA and protein. Both DNA and proteins are composed of chains containing repeating units. For DNA, these units are the C, T, A and G bases, and for proteins the units are 20 different amino acids. In both cases, the sequence of the repeating units is a critical part of the information carried by these molecules. In DNA, the sequence of bases forms the code that is converted to make protein, and for proteins the arrangement of amino acids determines the protein’s structure and function. For DNA, copies of the DNA to be sequenced are made and labeled with fluorescent markers before they are identified using a sequencing machine. For proteins, single amino acid residues are removed from one end of the protein and identified one at a time using an automated system.