Scrapie is an ovine transmissible spongiform encephalopathy, and its susceptibility is associated with polymorphisms in the prion protein gene (PRNP). Genetic selection is currently the most effective mean for eradication of the susceptible VRQ allele in favour of resistant ARR allele. Maintenance of genetic diversity should be one of the major objectives in breeding programmes, especially in endangered breeds, and genetic information are an excellent alternative to pedigree data where these information are missing. The aim of our study was to determine changes of genetic variability in six native sheep breeds from autonomous province of Bolzano, northern Italy, following simulation of scrapie selection scenarios. A total of 684 rams were investigated for PRNP polymorphisms and for 10 microsatellite loci to estimate genetic variability. Across all loci, a total of 163 alleles were detected with a mean of 10.4 alleles per locus. Average observed (Ho) and unbiased expected (uHe) heterozygosity overall loci were 0.74 and 0.78, respectively, showing a statistically significant deviation from Hardy-Weinberg equilibrium (HWE) in all breeds. This heterozygosity deficit was confirmed by a positive fixation index (Fis), determining a moderate inbreeding in each breed. Simulating a soft selection, where only rams having at least a VRQ allele should be excluded from reproduction, Ho, uHe and Fis values remained almost unchanged, indicating that genetic variability should not be affected by the removal of these individuals. With a mild selection scenario, considering only rams with at least one ARR allele, we observed a decrease in the mean alleles per breed (8.9) and the maintenance of heterozygosity deficiency, except for two breeds, where it was any longer significant. These results showed that selection strategies allowing use of heterozygous as well homozygous ARR rams might be the right compromise to improve resistance to scrapie and to do not dramatically affect genetic variability of these breeds.

中文翻译：

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博尔扎诺省（意大利北部）六个本土绵羊品种选择抗痒病后的遗传变异性

痒病是一种绵羊传染性海绵状脑病，其易感性与朊病毒蛋白基因 (PRNP) 的多态性有关。遗传选择是目前根除易感 VRQ 等位基因以支持抗性 ARR 等位基因的最有效方法。保持遗传多样性应该是育种计划的主要目标之一，尤其是在濒危品种中，遗传信息是缺少这些信息的谱系数据的绝佳替代品。我们研究的目的是在模拟痒病选择场景后，确定来自意大利北部博尔扎诺自治省的六个本地绵羊品种的遗传变异性变化。总共研究了 684 只公羊的 PRNP 多态性和 10 个微卫星位点以估计遗传变异性。在所有基因座中，总共检测到 163 个等位基因，每个基因座平均有 10.4 个等位基因。平均观察 (Ho) 和无偏预期 (uHe) 杂合性总体位点分别为 0.74 和 0.78，显示所有品种与哈迪-温伯格平衡 (HWE) 的统计显着偏差。这种杂合性缺陷由正固定指数 (Fis) 证实，确定每个品种的中等近交。模拟软选择，其中只应将至少具有 VRQ 等位基因的公羊排除在繁殖之外，Ho、uHe 和 Fis 值几乎保持不变，表明去除这些个体不应影响遗传变异性。在温和的选择场景中，仅考虑具有至少一个 ARR 等位基因的公羊，我们观察到每个品种的平均等位基因减少 (8. 9）和杂合性缺陷的维持，除了两个品种，它不再显着。这些结果表明，允许使用杂合子和纯合子 ARR 公羊的选择策略可能是提高对痒病的抗性并且不会显着影响这些品种的遗传变异性的正确折衷方案。