Linked Genes, Pseudoalleles and Blood Groups

Abstract

The theory of closely or absolutely linked genes and of "pseudoallelic" genic elements as applied to blood groups is critically examined both at the level of the antigen and at the level of the gene. The most complex system of blood groups recognized to date in any species, namely the "B" system of cattle, is used as a model throughout the discussion. Comparisons are drawn between certain features of the B system and the Rh system of man in regard to the kind of explanation involved in the "CDE" symbolism of the Rh blood groups. At the outset it is pointed out that the notion of linked genes and/or pseudoalleles traces to the erroneous impression that a single specificity is the definitive characteristic of an antigen. Hence, the theory of linked genes has constituted a problem in the study of blood groups only insofar as it has led to confusion in interpreting serological results. The hypothesis of multiple alleles proposed to explain the more complex systems of blood groups still exist and can be maintained even though the time may come when "crossover" mutants are recognized and differentiated from mutations in these alleles caused by other forces.