From the following phenotype Anti-D +, Anti-C +, Anti-E +, Anti-c +, Anti-e +, what is the most common genotype?

• A. rr
• B. dCE/dCE
• C. CDE/cde
• D. R^1r

Answer: (C)

RhCE antigens are determined by two haplotypes inherited at the RhCE/D locus, and their effects are codominant. To have D, C, E, and also c and e antigens on red cells, one chromosome must carry the CDE haplotype (D+, C+, E+) and the other must carry the reciprocal cde haplotype (lacking D, C, E but providing c and e). That CDE/cde combination is the most common way to obtain a red cell surface expressing all five RhCE antigens: D+, C+, E+, c+, and e+. The other genotypes would miss one or more antigens (for example, a D-negative combination or lacking one of the antigens), so they don’t produce the same complete phenotype as often.