Figure 2. Genotyping by diagnostic restriction enzyme digestion. The single-based deletion associated with O alleles (position 258) creates a Kpnl site (O allele) and eliminates the BstEII site (A/B allele). Three or 4 nucleotide substitutions between A and B allelic cDNA can also be identified by diagnostic enzymes. For genotyping, polymerase chain-reaction (PCR)-amplified DNA was analyzed by diagnostic enzyme digestion (Yamamoto et al., 1990).