Phenogroups and quantitative allelic expression for rabbit serum α₂-macroglobulin allotypes

Abstract

The four allotypic specificities, z1, z2, y3, and y4, of rabbit α ₂ -macroglobulin (α ₂ M) were found to be inherited as three phenogroups, z1y3, z1y4, or z2y3. The phenogroup inheritance can be viewed as reflecting the close linkage of two loci, i.e., the Mtz locus with the z ¹ and z ² alleles and the Mty locus with the y ³ and y ⁴ alleles. Radioimmunoassay of α ₂ M by an indirect precipitation method confirmed our earlier studies by a direct method showing that nearly all molecules of z1 or z2 homozygotes possess either z1 or z2, respectively, and that most molecules in the heterozygote are hybrids with both z2 and z2. Unlabeled α ₂ M from homozygotes and heterozygotes was used to competitively inhibit the reaction of anti-z1 or anti-z2 with labeled α ₂ M. This revealed that z1z2 heterozygotes possess approximately 35% of the z1 and 64% of the z2 determinants found in the respective homozygotes. These results resemble previous observations with the y3 and y4 allotypes which indicated an unequal contribution of allelic genes in the formation of rabbit α ₂ M and the lack of allelic exclusion in most of the molecules. Unlike immunoglobulins and low-density lipoproteins, hybrid α ₂ M molecules form by the interaction of homologous chromosomes.