Group A and B Subgroups

The serum of group B persons contains two antibodies: anti A and anti A₁. By proper absorption, the two antibodies can be separated. Cells of group A that react with anti A₁ are part of the subgroup A₁. Cells that react with anti A but not with antiA₁  fall into subgroups weaker than A₁, thus being classified as A₂.

Subgroup A_{1 : Makes up to 80 Percent of the A gene pool and most of the H is changed to A antigen because of the large number of antigen sites on the cells.}

Subgroup A_{2: make up 20 percent of the A gene pool, and have less H changed to A antigen because of the smaller amount of sites on the cells compared to A1. Could produce anti A1.} 

*** Subgroups of B are rare in most populations. They are usually recognized by variations in the strength of a reaction with anti B. There is no reagent available to distinguish among them. The patient’s serum may contain anti B antibodies.

ABO antibodies and antigens

Antibodies produced by exposure to antigens  (bacteria and plants) are not seen until four to six months old. The anti A and anti B found in the serum of a newborns is of maternal origin. In healthy individuals, ABO antibodies are always present peaking at age five to ten years.

Percentage of ABO Antigens and Antibodies in United States Populations

***ABO antigen frequency can vary in other populations with different ethnic mixes.

Link

Genotype Diet, Allergies, etc. for A1, A2, B, & O Types