What does the genotype rr indicate in terms of C antigen status?

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What does the genotype rr indicate in terms of C antigen status?

In the C/c gene system, whether the C antigen is present on red cells depends on the combination of alleles you inherit. A single dominant C allele is enough to express the C antigen, so CC or Cc individuals show the C antigen. Only when both alleles are recessive and there is no C allele at all do you fail to express C. Therefore, having two recessive alleles (rr) means no C antigen is produced on the red cells. This is what “homozygous for absence of C antigen” describes. The result is a C antigen–negative phenotype. (The D antigen status is a separate Rh factor and isn’t determined by this same C/c locus.)

In the C/c gene system, whether the C antigen is present on red cells depends on the combination of alleles you inherit. A single dominant C allele is enough to express the C antigen, so CC or Cc individuals show the C antigen. Only when both alleles are recessive and there is no C allele at all do you fail to express C.

Therefore, having two recessive alleles (rr) means no C antigen is produced on the red cells. This is what “homozygous for absence of C antigen” describes. The result is a C antigen–negative phenotype. (The D antigen status is a separate Rh factor and isn’t determined by this same C/c locus.)

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