The subgroups of the B antigen are not as numerous or as common as that observed for those of the Subgroups of Type A. The lower frequency of B subgroups in the general population is also a result of the lower frequency of blood group B in general. Like Subgroups of Type A, the subgroups of the B blood group are predominantly a result of changes in the genetic sequence of the B allele at the ABO locus of chromosome 9q34. The result is a decrease in the quantity of B antigen produced. The use of polyclonal typing sera will show variable reaction strengths with the variant B antigen.
The nomenclature of the B subgroups is also consistent with that used for the A Subgroups. The "main" B Subgroups identified are: