Table 2-10. Determination of some Rh phenotypes from typing results.
(2) Using the phenotype and knowledge of how frequently particular
antigenic combinations derive from a single allele or gene complex, one can make
useful assumptions about presumed genotypes. This is important in population studies,
in studies to assign parentage, and in evaluating hemolytic disease of the newborn
resulting from anti-Rho(D). There is no simple serologic technique for distinguishing
among persons with two genes which code for Rho(D) (homozygous Rh-positive) and
those with one gene that codes for Rho(D) and one gene whose product lacks Rho(D)
(heterozygous Rh-positive), since the Rho(D) antigen is fully expressed even when
there is only one gene present that determines the trait. There is no antiserum that
specifically reacts with the product of the "Rh-negative" gene. (This would be anti-d, but
the d antigen has never been shown to exist.) The person whose cells are Rh-negative
obviously has two genes which code for a surface configuration that lacks Rho(D).