Figure 3

Schematic illustration of the effect of introns involved in SNP genotyping. In the first case, all the genotyping primers are located in the same exon nearby, leading to successful genotyping (+); in the second case (middle), one of the genotyping primers (P3 as shown) was located at the exon-intron border, causing non-base pairing that lead to failure of genotyping (-); and in the third case, even though all primers were located in exon regions. However, an intron was involved that demands PCR extension to across the intron. Apparently, the Bead array technology provide very limited extension capability, leading to genotyping failure (-) as well.