Genomic hybridization of bovine class II major histocompatibility genes: 1. Extensive polymorphism of DQ alpha and DQ beta genes.

Class II genes of the bovine major histocompatibility complex (MHC) were investigated by Southern blot analysis using human cDNA probes for DQ alpha, DQ beta, DR alpha and DR beta. The presence of a DQ-like and a DR-like subregion in cattle was clearly indicated. Highly polymorphic restriction fragment patterns were obtained when genomic DNA, digested with any one of the BamHI, EcoRI or PvuII restriction enzymes, was hybridized with the DQ alpha and the DQ beta probe. The polymorphisms were interpreted genetically by analysing five paternal half-sib families of the Swedish Red and White breed. The material comprised, besides the bulls, 28 offspring and their dams. The analysis resolved 9 and 12 allelic variants of DQ alpha and DQ beta respectively. Thus, this investigation establishes a method for routine typing of MHC class II gene polymorphism in cattle. The results were entirely consistent with close linkage of DQ alpha and DQ beta since no recombinant was found and since alleles at these loci occurred in complete linkage disequilibrium in the material investigated. Close linkage between DQ and the blood group locus M, which has previously been found to be closely linked to the serologically defined BoLA-A locus, was also indicated. In this study DNA was isolated from frozen semen samples of dead bulls, which shows that this type of analysis will be useful in genetic investigations in cattle breeds, where artificial insemination is practised.