Phylogenetic analysis of intron 5 of the ABO gene. The phylogenetic analysis has been done using Treecon version 1.3b.^18,19  The unrooted tree has been used in order to describe the relative genetic distance between the sequences. The length of the branches represents the extent of nucleotide differences between the lineages. The topology of the tree suggests 5 main lineages for nucleotide sequence diversity in intron 5: ABO*A, ABO*B, ABO*O01, ABO*O02, and ABO*O03. The major ABO alleles are indicated by rectangles.