Which theory postulates that the Rh system antigens were produced by three closely linked sets of alleles?

• A. Fisher-Race
• B. Parker-Weinberg
• C. Landsteiner
• D. Haldane-Smith

Answer: (A)

The Rh antigen pattern is explained by three closely linked gene loci on the same chromosome—the D/d, C/c, and E/e pairs. Each locus contributes a specific antigen variant, and the combination present on a chromosome defines the Rh phenotype. Because these loci are tightly linked, they are usually inherited together as a single haplotype, so certain Rh antigen sets appear together across individuals. This idea is the Fisher-Race theory. It accounts for how the D, C/c, and E/e antigens are expressed in linked combinations on red cells. Other models exist historically, but the three-loci, tightly linked concept is the one described here.