參考
http://bioinfogeek.over-blog.com/2017/09/gene-expression-units-explained-rpm-rpkm-fpkm-and-tpm.html
https://media.nature.com/original/nature-assets/nature/journal/v490/n7418/extref/nature11450-s1.pdf
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5407692/
https://cloud.tencent.com/developer/article/1455921
RPKM：Reads Per Kilobase Million宣渗；
103?normalizes for gene length and 106?for sequencing depth factor.
基因長(zhǎng)度10的3次方標(biāo)準(zhǔn)化互婿，測(cè)序深度10的6次方
FPKM：(Fragments per kilo base per million mapped reads)?
區(qū)別僅在于，F(xiàn)ragment 與 Read非剃。RPKM針對(duì)早期的SE測(cè)序，F(xiàn)PKM則是在PE測(cè)序上對(duì)RPKM的校正推沸。在PE中备绽，一個(gè)Fragments測(cè)兩端，會(huì)得到2條Reads鬓催，但由于后期質(zhì)量或比對(duì)的過(guò)濾肺素，有可能一個(gè)Fragments的2條Reads最后只有一條進(jìn)入最后的表達(dá)量分析∮罴荩總之倍靡，對(duì)某一對(duì)Reads而言，這2條Reads只能算一個(gè)Fragments课舍，所以塌西，F(xiàn)ragment的最終數(shù)目是Reads的1到2倍之間他挎。
TPM (Transcript per million)
TPM 考慮了基因長(zhǎng)度
TPM does not count for total number of mapped reads
TPM proposed as an alternative to RPKM due to inaccuracy in RPKM measurement?
(Wagner et al., 2012)
TPM is suitable for sequencing protocols where reads sequencing depends on gene length
RPM (Reads per million mapped reads)
