A.
The ABO gene is located on chromosome 9q34.
B.
The ABO gene is fairly large, consisting of night exons spread over 18 kb.
C.
The open reading frame of the protein is located primarily in exons 6 and 7.
D.
ABO expression is also regulated by the H gene, which is responsible for the synthesis of H antigen substrate, the precursor of A and B antigens.