Sequencing results of the exon 3–intron 3 junction of the ABO genes of a common group B individual and the B₃ propositus.

Genomic DNAs were purified from an individual with common group B phenotype and an individual with B₃ phenotype. The regions from exon 2 to intron 3 of the ABO genes were amplified by PCR, and the sequences were analyzed by direct sequencing. The sequencing results of the exon 3–intron 3 junctions of the common group B (left panel) and the B₃ (right panel) samples are shown. In the B₃ sample, a heterozygous state for G and A nucleotides (underlined) at the +5 position of intron 3 was demonstrated. A dashed line indicates the conserved sequence of the splice donor site.