GENETIC AND PATHOLOGICAL ASPECTS OF PRION PROTEIN (PrP) IN SHEEP BELONGING TO BOTOSANI KARAKUL BREED

摘要

By Real-Time PCR technique, the existence of polymorphism at the level of PrP gene (associated with susceptibility to scrapie) has been revealed in Botosani Karakul sheep. Practically, the polymorphism was analyzed at codons 136, 154 and 171. Among the five alleles (ARR, ARQ, AHQ, ARH and VRQ) incriminated in association with this disease in ovine species, only three of them were found in the Botosani Karakul breed determining the phenotypic expression of all six possible genotypes. The most common allele is ARQ (56.10%); the incidence of allele ARR (38.21%) is considerable, and the allele ARH has a low prevalence (5.69%). The most frequent genotype is ARQ/ARQ (47.97%), followed by genotype ARR/ARR (26.83%); the genotypes ARR/ARQ (14.63%) and ARR/ARH (8.13%) record moderate or relatively low frequencies, the other two genotypes (ARO/ARH = 1.63% and ARH/ARH = 0.81%) being met rarely in the population. The distributions of genotypes at the PrP locus make the total homozygosity (75.61%) to be well represented compared to the total heterozygosity (24.39%). In the Botosani Karakul breed, major discrepancies were observed between the empirical frequencies and those estimated, so that we witness a very significant genetic disequilibrium Hardy-Weinberg at the PrP locus. In the Botosani Karakul sheep, the prion genotypes that are associated in the highest degree with scrapie are completely absent (classes of risk R4 and R5). Thus, all individuals are resistant to scrapie (50%) (classes of risk R1) or have a low risk of contracting the disease (50%) (class of risk R3). This association represents a notable selective advantage of Botosani Karakul sheep compared to all other autochthonous or foreign sheep breeds.