RH and RH50 genotypes of family YT. RH50 alleles are as follows: +, wild-type carrying a G at nt 836; s, transcriptionally silent allele carrying a G at nt 836; *, mutant allele carrying an A at nt 836. The RH genotype of the Rh_null propositus Y.T. is shown in brackets since it is not phenotypically expressed.