測序是指描述DNA或蛋白質中重復單位的序列。DNA和蛋白質都是由包含重復單位的鏈組成。對DNA來說，這些單位是C、T、A和G堿基，對蛋白質來說這些單位是20個不同的氨基酸。這些重復單位的序列是其所攜帶信息的重要部分。組成DNA的堿基序列構成合成蛋白質的密碼，而蛋白質中氨基酸的排列決定了蛋白質的結構和功能。在用測序儀對DNA測序前要對其進行復制和熒光標記。蛋白質自動測序系統從蛋白質一端每次切下一個氨基酸殘基并識別。

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.