The location ofC2, C4, andBF relative toHLA-B andHLA-D

Abstract
The loci forHLA-A, B, C, D, andDR are known to be closely linked to the structural loci for the complement components C2, BF, and the duplicated loci for C4, C4A and C4B. Conflicting evidence has been presented for the order of these genes. However, new techniques have made possible identification of markers in theHLA-D andC4 region for nearly all identified haplotypes. In our population we have confirmed fiveHLA-B-D crossovers and in each case informative allotypes of C2, BF, or C4A and C4B segregated withHLA-D orDR suggesting that the loci for these proteins lie close toHLA-D andDR. These findings may be of importance for resolving problems encountered in the assignment ofHLA-D alleles.