Disequilibrium linkage (gametic disequilibrium) of structural genes in the bovine population

In the population of Kholmogor cattle (n=824), gametic disequilibrium was studied for alleles of the polymorphic loci β-Lg (LGB), β-Cn (CSN2) and æ-Cn (CSN3). In purebred Kholmogor cattle, the β-casein polymorphism is determined by three alleles with the frequencies of CSN2 А 1 – 0.368±0.0076, CSN2 А 2 – 0.497±0.0078, CSN2 B – 0.136±0.0056 and the frequencies of acasein of CSN3 А – 0.689 ±0.0061, CSN3B – 0.311±0.0061, respectively. The beta-lactoglobulin polymorphism is controlled by two alleles LGBA and LGB B with a frequency of 0.237±0.0048 and 0.763±0.0048, respectively. In the population of breeding plants, the gametic disequilibrium was revealed according to the alleles of loci CSN2 and LGB; CSN2 and CSN3. The factor that caused the gametic disequilibrium was probably the initial difference between native Russian cattle and black-and-white cattle of Western Europe on the basis of which the Kholmogor breed gene pool was developed. The population showed an excess of haplotypes β-Cn В æ-Cn В , β-Cn В β-Lg В (the "attraction" phase), apparently inherited mainly from native Russian cattle, and β-Cn А 1æ-Cn А , β-Cn А 2β-Lg А characteristic mainly for black-and-white cattle of Western Europe and a lack of β-Cn В æ-Cn А , β-Cn В β-Lg А (the "repulsion" phase), probably due to the low frequency of these haplotypes in both initial breeds. The role of various factors in the occurrence and maintenance of gamete disequilibrium is discussed. It is suggested that for alleles of non-linked loci, longtime retention of gametic disequilibrium in population is most likely supported by selection