Fisher and Race hypothesis: Rh factor involves three different pairs of alleles located on three different closely linked loci on the chromosome pair. This system is more commonly in use today, and uses the ‘Cde’ nomenclature. In the given figure, three pairs of Rh alleles (Cc, Dd and Ee) occur at 3 different loci on homologous chromosome pair-1.

The possible genotypes will be one C or c, one D or d, one E or e from each chromosome. For e.g. CDE/cde; CdE/cDe; cde/cde; CDe/CdE etc. All genotypes carrying a dominant ‘D’ allele will produce Rh+positive phenotype and double recessive genotype ‘dd’ will give rise to Rh negative phenotype.

Wiener Hypothesis: Wiener proposed the existence of eight alleles (R¹ , R² , R⁰ , R^Z , r, r¹ , r¹¹ , r^Y ) at a single Rh locus.

All genotypes carrying a dominant ‘R allele’ (R1 , R² ,R⁰ ,R^Z ) will produce ‘Rh-positive’ ^phenotype and double recessive genotypes (rr, rr¹ , rr¹¹ , rr^Y ) will give rise to Rh-negative phenotype.