Schematic illustration of the multiplex genotyping procedure. Only one SNP is shown. Primers and probes are shown as arrowed lines. Microarray spots are indicated as ellipsoids. (A) Amplification of the polymorphic sequence. Two allelic sequences use the same set of primers, P1 and P2. (B) Generation of ssDNA by using the primer-probes in both directions in separate tubes. Only the two allelic template strands in each reaction are shown. (C) ssDNA generated from B. (D) Addition of the ssDNA to the respective microarrays containing probes in different directions. (E) ssDNA templates hybridized to their probes on the microarrays. (F) Labeling probes by incorporating fluorescently labeled ddNTPs. (G) Labeled probes after washing off all other reagents.