Unlike most other blood groups, the two antigens are not encoded by different alleles; rather, I-branching enzyme converts i antigen to I antigen by adding branches. The gene encoding I-branching enzyme is located on chromosome 6.
Unlike most blood groups, both antigens are not produced by different alleles; rather, they undergo a transformation through an I-branching enzyme that introduces branches onto the i antigen to form the I antigen. The location of this gene encoding the I-branching enzyme is on chromosome 6.