Functional annotation is defined as the process of collecting information about and describing a gene's biological identity—its various aliases, molecular function, biological role(s), subcellular location, and its expression domains within the plant.功能注释就是找到gene对应的功能，在上一步骤中找到的是gene structure feature，现在需要找到gene functional feature 。gene仅仅是大类上的gene，但是未知这个gene在更细小分支上的作用，比如在某种代谢通路中的作用。
- The DNA in our chromosomes contains genes that get transcribed into RNA.
- There are several different types of RNA (tRNA, mRNA, rRNA, etc.). They are composed of the same building blocks but have different functions, locations and structures.
- Messenger RNA (mRNA) may be translated into a protein. The standard information flow is:
- DNA→RNA→Protein
- The set of genes that are 'on' at any given time is critical. Different genes need to be 'on' at different times depending on the needs and functions of any particular cell
- 因为相同gene structure but different gene function,所以为了鉴定出真实的gene function需要采用functional annotation