First chemistry cycle: determine first base To initiate the first sequencing cycle,add all four labeled reversible terminators,primers,and DNA polymerase enzyme to the flow cell. Before initiating the Image of first chemistry cycle next chemistry cycle After laser excitation,capture the image The blocked 3'terminus of emitted fluorescence from each and the fluorophore cluster on the flow cell.Record the from each incorporated identity of the first base for each cluster. base are removed. Laser GCTGA... A Sequence read over multiple chemistry cycles Repeat cycles of sequencing to determine the sequence of bases in a given fragment a single base at a time.Illumina Genome Analyzer