Outliers with highly superior performance are valuable in plant breeding, but their distribution in populations has not been well-studied. My objectives were to determine (a) if outliers behave in a predictable manner; (b) if they are distributed according to a normal distribution as is assumed for quantitative traits; and (c) which parental characteristics are indicative of the best chances of getting progeny with extreme performance. All possible biparental populations were made among 15 simulated barley (Hordeum vulgare L.) parental lines in BreedingGames software. Ten million lines were simulated within each cross for a total of 1.05 billion lines. Within each biparental population, recombinant inbreds in the top 1.0, 0.1, and 0.01% tails had a continuous distribution, indicating that outliers behave in a predictable manner but are rare in practice only because the population sizes used in breeding are small. Having a finite number of loci led to slight kurtosis, which caused a minor upward bias when the usefulness criterion was applied to the extreme upper tails. The midparent value was an excellent indicator of which biparental crosses had high upper-tail means, to the extent that modeling the genetic variance within each biparental population had little added benefit. In the simulations, selection for protein concentration and Fusarium (F. graminearum) head blight resistance decreased the gains for yield and changed the biparental population that led to the highest yield gains. Results indicated that having one very large breeding population in a select-only scheme is inferior to two or more select-and-recombine cycles with smaller populations.

中文翻译：

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异常值及其在繁殖种群中的分布

具有高度优越性能的异常值在植物育种中很有价值，但它们在种群中的分布尚未得到充分研究。我的目标是确定 (a) 异常值是否以可预测的方式表现；(b) 如果它们按照数量性状假设的正态分布进行分布；(c) 哪些亲本特征表明获得具有极端表现的后代的最佳机会。所有可能的双亲群体都是在BreedingGames中的 15 个模拟大麦 ( Hordeum vulgare L.) 亲本系中制作的软件。每个十字架内模拟了 1000 万条线，总共有 10.5 亿条线。在每个双亲群体中，前 1.0、0.1 和 0.01% 尾部的重组近交系具有连续分布，这表明异常值的行为是可预测的，但在实践中很少见，只是因为用于育种的群体规模很小。具有有限数量的基因座会导致轻微的峰度，当有用性标准应用于极端上尾时，这会导致轻微的向上偏差。中亲值是一个很好的指标，表明双亲杂交具有较高的上尾均值，在某种程度上，对每个双亲群体内的遗传变异进行建模几乎没有额外的好处。在模拟中，选择蛋白质浓度和镰刀菌（F. graminearum) 头枯病抗性降低了产量的增加并改变了导致最高产量增加的双亲种群。结果表明，在仅选择方案中拥有一个非常大的育种群体不如具有较小群体的两个或更多个选择和重组循环。