Median-joining haplotype network inferred from all 154 ABO sequences. Phylogenetic network showing the evolutionary relationships among ABO haplotypes. Each circle represents a unique haplotype with the size being proportional to the number of sequences represented. Haplotype circles are colored according to the ABO allele groups; black dots represent missing intermediate haplotypes (ie, unsampled, likely ancient haplotypes). Mutational steps between haplotypes are displayed as hatch marks along the connection lines. The length of the connection lines is not scaled by phylogenetic distance.