Figure 3.

Illumina sequencing process. (A) DNA library. Breaks the genome DNA to form DNA fragments, adds adapters at both ends, and constructs a single-stranded DNA (ssDNA) library. After adding DNA library into flowcell, DNA fragments will be attached to the surface of flowcell when passing through flowcell. (B) Bridge PCR. Each DNA fragment is clustered in its position. After bridge amplification, each cluster contains many copies of the ssDNA template. (C) SBS: DNA polymerase, primers, and four dNTPs with specific fluorescence are added to the reaction system at the same time. The 3′ end of these dNTPs is connected with an azide group, which can block the incorporation of the next base, so only one base can be extended at a time. After washing off the remaining dNTP and enzyme with water, photos are scanned. After scanning, add chemical reagent, cut off the azide group and quenching fluorescence, and next cycle. (D) Fluorescent signal reception.