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35 36 | Chapter 4 one producing D or no D, the other producing C or c and E or e. Shortly after, Tippett’s theory was validated by molecular genetic studies. Haplotypes, genotypes, and phenotypes Although there are only two Rh gene loci, RHD and RHCE, the Fisher– Race theory of three loci, D/d, C/c, and E/e, is still appropriate for interpreting serological data because C/c and E/e represent different ­ mutation sites within RHCE. No conclusive evidence of recombination between D/d and C/c, C/c and E/e, or D/d and E/e has been found.

2 and 15), yet numerous ­individuals with these variants have been found who have made anti-D. Some partial D antigens, such as DVI, have distinctly weakened ­expression of those epitopes they have. Consequently, the terminology is ­misleading and a new terminology is required. 3 provides a list of some of the symbols currently used to describe D variants. Another type of D variant is DEL, in which the D is expressed so weakly it cannot be detected by conventional serological methods and requires special techniques, in particular adsorption and elution.

Below this are diagrammatic representations of Rh proteins, showing the N- and C-termini, the 12 membrane-spanning domains, and the six extracellular loops. The C/c and E/e polymorphisms are determined primarily by amino acid substitutions on the second and fourth (from the N-terminus) extracellular loops of the RhCcEe protein. Above: D+ haplotype. Below: D− (deletion) haplotype. Within the red cell membrane, the Rh proteins are associated with a glycoprotein called the Rh-associated glycoprotein (RhAG).