Examples of cyclic array sequencing and sequencing by hybridization.

(A) Schematic of cyclic-array sequencing-by-synthesis methods (for example, fluorescent in situ sequencing, pyrosequencing, or single-molecule methods). Left: repeated cycles of polymerase extension with a single nucleotide at each step. The means of detecting incorporation events at individual array features varies from method to method. The sequencing templates shown here have been produced by using the POLONY method. Right: an example of raw data from Pyrosequencing, a cyclic-array method. The identity of nucleotides used at each extension step are listed along the x-axis. The y-axis depicts the measured signal at each cycle for one sequence; both single and multiple (such as homopolymeric) incorporations can be distinguished from non-incorporation events. The decoded sequence is listed along the top. (B) Sequencing by hybridization. To resequence a given base, four features are present on the microarray, each identical except for a different nucleotide at the query position (the central base of 25-bp oligonucleotides). Genotyping data at each base are obtained through the differential hybridization of genomic DNA to each set of four features.