GenFlex Tag Array genotyping. The system consists of 2050 tag probe locations, designed to have approximately equal hybridization characteristics. (A) DNA encompassing each SNP is amplified with a set of primers and then (B) interrogated in a single-base extension reaction in solution with a primer attached to a tag complementary to a unique tag probe on the GenFlex Tag Array chip (C). Different alleles of a given SNP can be discriminated by use of sequence-specific dideoxynucleotides labeled with either fluorescein or biotin. The biotinylated positions are then labeled indirectly by reaction with streptavidin-conjugated phycoerythrin or SAPE after hybridization of the tag-SBE products to the tag probes. (D) Laser-induced emissions from the chips are then scanned at both 530 and 570 nm.