Multiple Alleles and the ABO Blood Groups
(Canadian Campbell 2nd ed -Page 292)

The discovery of human blood groups was reported by Dr. Karl Landsteiner in 1900, and for this important discovery he was awarded the Nobel Prize in Medicine and Physiology. Landsteiner's work led to the establishment of the four common blood groups O, A, B and AB. The basis for the four blood groups is the presence of naturally occuring antigens and antibodies in the blood of individuals in various combinations. In the ABO blood groups the factors that determine the antigens and antibodies are inherited, the antigen appearing in the offspring only if present in at least one parent. The two antigens that were discovered by Landsteiner are called A and B and are found on the surface of the erythrocytes. The antibodies are found in the serum and they are known as anti-A and anti-B. The antigens determining the four blood groups are the result of the expression of three alleles; O, A and B; the latter two being dominant to O. The genotypes AA and AO, and the genotypes BB and BO cannot be distinguished serologically and are classified as group A and B respectively. Thus only four phenotypes (A, B, AB, and O) can be recognized, although six genotypes occur.

The Human Blood Groups

Cells with antigen A on the surface are agglutinated (cells clump together) by anti-A antibody; cells with antigen B on the surface are agglutinated by anti-B antibody. The degree of agglutination depends upon other factors such as the concentration of antibodies in the serum. When blood is given in a transfusion, the kind of antigen of the donor and antibody of the recipient are all that matter. The reason for this is that the antibodies of the donor are so diluted by the blood of the recipient that they are not effective in agglutinating the recipients antigens. Despite this exact matches are the rule except in emergency situations. Compatibility means that the recipient and donor in a transfusion belong to the same group and furthermore, that any possibility of additional reactions has been eliminated. There are many other blood grouping systems known in addition to the ABO series; for example the N and M series and the well known Rh⁺ and Rh^- groups.

What types of children are not possible from two AB or two 0 parents?

In a case of disputed paternity, the child is group O, the mother group A, and the putative father is AB. What can you conclude from this information?

What if the putative father were group B?

First published Sept 95: Modified June 2019
Copyright © Michael Shaw 2019 (Images and Text)

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