Fig. 3.

Variations of inDrop library structures from the perspective of sequencing. a A standard Illumina library contains P7 and P5 adapter sites that are used to bind Illumina sequencing flow cells. i7-and i5-indexes are incorporated onto the P7 and P5 sides, respectively, to adopt a dual-indexing strategy. On either side of the insert are sites (R1 and R2) where standard Illumina sequencing primers are used to read across both sides of the insert. The reverse complement of these read priming sites then allows for the priming and subsequent reading of the i7 and i5 sample indexes. b The inDrop V2 library structure also incorporates the P7 and P5 flow cell adapter binding sites, with a single i7 index. The V2 structure utilizes a R1 priming site that is a truncated version of the standard R2 priming site, and a R2 priming site that is a deprecated R2 priming site. In addition, the R1 and R2 of the V2 structure are flipped so that the insert is read backwards from a normal Illumina library. c The TruSeq-inDrop (TruDrop) structure incorporates a second (i5) index and the standard Illumina R1 and R2 priming sites that are used in all Illumina TruSeq libraries