Mariuca A. Population-genetic mechanisms of adaptation and distribution of semi-letha recessive mutation on tne e[ample of BLAD in cattle

In the dissertation with the purposes of finding out of the possible mechanisms of distribution of semi-lethal mutations in cattle, in particular, bovine leukocyte adhesiveness deficiency (BLAD) in Holstein breed, the heterozygosity comparison on the number of genetic-biochemical systems of animal's groups, which carried BLAD mutation and were free from it was carried out. The increase of mutation BLAD carriers in Ukrainian economies from 1995 to 2003 yy was revealed. The association of heterozygosity of BLAD presence with the increased heterozygosity on such genetic-biochemical systems, as a receptor to vitamin D, purine nucleoside phosphorylase was marked. It was shown that the heterozygosity increase was connected to influence of the factors of natural selection, promoting heterozygote accumulation on genetic-biochemical systems. For comparison of it the carriers of heterozygote in the kappa - casein (CSN3) locus was investigated. A number of autochthonous cattle breeds were included in investigation in relation with the low level of polymorphism of CSN3 in Holstein. The increased heterozygosity on the same genetic-biochemical systems in animals with CSN3 АВ genotype as in the BLAD carriers was observed. The obtained data testified that such mutations as BLAD and CSN3 B could be support by natural selection promoting reproduction of heterozygous animals, and the frequency of them could decrease under influence of artificial selection directed against some alleles, as in case of Holstein breed - against of allele CSN3 B.