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Combinations of four alpha-2-globulin allotypes were studied for their distribution in pigs of nine different breeds and hybrid groups. Based on this analysis, a new, previously unpublished polyallelic genetic system designated A2G was postulated. The complex alleles of this system control alpha-2-globulin allotypes and are suggested to be encoded by genes of two subloci. One of these subloci is virtually monomorphic, whereas the other has at least four allelic variants.

The results of genetic studies of transformation of alpha-macroglobullin (AM) allogroups (i.e., fixed allotype combinations) in pigs are presented. Population and hybridization studies showed that the phenomenon discovered was based on activation/inactivation of the AMI allotype expression, which depended on the genetic environment and interlocus relationships. Genetic and selection bases, as well as the significance of the transformation phenomenon described, are discussed.

Antibodies against a new allotype, Ld2, of mink low-density lipoprotein (LDL) were obtained by alloimmunization with a preparation of this lipoprotein. The two known allotypes of LDL, designated Ld1 and Ld2, are coded for by codominant alleles of the autosomal Ld locus. This locus is probably involved in the genetic control of the whole serum pool of LDL molecules. In Ld1/Ld2 heterozygotes, LDL is represented by two homozygous types of molecules, Ld1 and Ld2; it has no hybrid molecules bearing both allotypic specificities together. The results suggest that the Ld locus has, presumably, only two alleles in the mink populations studies. Mink LDL having allotypes Ld1 and Ld2 was found to be homologous to human and pig LDLs. Antigenic specificity of Ld1 allotype was established in the sera of a wide phylogenetic range of mammals and in the human LDL. The parallelism between the phylogenetic antiquity of the Ld1 gene and its high frequency in mink and other species may be attributed to the selective value of this gene, which has been retained unaltered during macroevolution.

A series of intraspecific immunizations of pigs by whole blood serum in complete Freund's adjuvant was performed. Four allo-antisera to different serum allotypes were obtained. These allotypes were assigned to A1, B1, C1 and D1. The results of identification show that the allotype A1 is probably a marker of immunoglobulin G. The allotypes B1, C1 and D1 were established to belong to different alpha-globulins, D1 being a marker of lipoprotein. Two geographically isolated populations of white large breed were tested. Two allotype combinations were found to be independent of one another and of sex. Significant differences in allotype frequency between two populations were only established for the G1 (F = 0.142 and 0.334; P less than 0.01). In both populations allotype B1 has the frequency 1.0, the frequencies of allotype A1 being 0.734 and 0.747. Most rare is the allotype D1 (F = 0.078 and 0.082).

An idea on organization of the Ld-system of low density lipoprotein in the domestic mink as on a "closed" immunogenetic system with two codominant alleles Ld1 and Ld2 was confirmed. Significant differences in frequencies of genes and genotypes of the Ld-system between state farm "populations" unaffected with Aleutian disease and those which were centres of this epizootic were established. The results obtained confirm the assumption made earlier on subvitality of the Ld2 gene.