The ABO alleles were aligned by their names. Only the differences (mutations/single nucleotide polymorphisms (SNPs)) from the A101 allele are shown on the appropriate nucleotide locations (5' to 3' of the gene is shown from left to right). The exon sequences are shown in dark gray and the intron sequences are shown in light gray. The locations of the four amino acid substitutions that discriminate A and B transferases are indicated by red arrows, and the O-allele specific single nucleotide deletion at nucleotide 261 is shown with a blue arrow. The small area of the table was enlarged and is shown in the bottom panel.