CRB: Shifts in the Genetic Load in Response to Inbreeding and Population Size in Brassica rapa

小行星9728855 小种群面临许多危险，包括遗传变异的丧失和近亲繁殖的遗传效应。 大多数人群 经历中度到重度的近亲繁殖衰退， 积累的有害突变通过近亲繁殖暴露出来。 人口 然而，有近亲繁殖史的人， 抑郁症，如果他们的突变负荷已经表达， 从人群中挑选出来。 一些科学家认为这种选择 能有效消除近亲繁殖的衰退， 通过有意的近亲繁殖来清除受威胁的种群。 另一些人则从理论上认为，在这种情况下， 在大多数情况下，实际上可能会增加轻度 有害突变在小群体中固定。 该项目将探索 选择是如何有效地清除真实的种群中的 近交衰退 为了节省空间并允许快速进展， 研究人员将使用卷心菜科的一种小型植物的品系 （芜菁）在实验室中培育生长迅速的。 多个品系将通过以下方式进行最大程度的近亲繁殖： 自我受精，而其他不同规模的人口将经历 自交与异交或纯异交交替6代。 然后，研究人员将估计有多少近亲繁殖抑郁症 在每一个处理下降，通过比较大小和性能， 从第一个， 第三代和第六代。 此外，他还将研究是否高 在来自近交系之间杂交的幼苗中预期的适合度是 保持在随后的几代随机交配（结果表明， 或说，是一种“恶”，或说，是一种“恶”。 暂时杂种优势）。 为了解决另一个争议，研究人员 还将比较当植物 在不同的生长条件下生长。 这些实验应该能证明近亲繁殖能多快、多彻底地清除种群的遗传负荷。 实证结果 这些应该有助于解决关于如何有效地 以及它能多快起作用。 这样的结果将帮助我们 为了了解交配系统是如何包含自交和 异型杂交进化。 他们还将阐明面临的遗传危害， 小种群，并证明故意近亲繁殖是否可以 为受威胁的小种群提供有用的繁殖策略， 濒危物种

9728855 Waller Small populations face many hazards including the loss of genetic variation and the genetic effects of inbreeding. Most populations experience moderate to severe inbreeding depression which occurs when accumulated deleterious mutations are exposed via inbreeding. Populations with a prior history of inbreeding, however, may experience less inbreeding depression if their load of mutations has already been expressed and selected out of the population. Some scientists argue that such selection can effectively eliminate inbreeding depression, allowing opportunities to purge threatened populations of their load via intentional inbreeding. Others argue from theory that purging will be weak and ineffective under most circumstances and may actually increase the number of mildly deleterious mutations fixed in small populations. This project will explore just how effectively selection can purge real populations of their inbreeding depression. To save space and allow rapid progress, the investigator will use strains of a small plant in the cabbage family (Brassica rapa) that has been bred to grow quickly in the laboratory. Multiple lines will be subjected to maximal inbreeding via self-fertilization, while other populations of various size will experience alternating selfing and outcrossing or pure outcrossing for six generations. The investigator will then estimate how much inbreeding depression has declined in each treatment by comparing the size and performance of seedlings derived from self- and cross-fertilized seeds from the first, third, and sixth generations. In addition, he will examine whether the high fitness expected in seedlings derived from crosses among the inbred lines is maintained over subsequent generations of random mating (a result suggesting that purging was effective) or deteriorates (reflecting the decay of temporary hybrid vigor). To address another controversy, the investigator will also compar e the amount of inbreeding depression observed when plants are grown under different growing conditions. These experiments should demonstrate how quickly and completely inbreeding can purge populations of their genetic load. Empirical results like these should help to resolve the controversy over how effective purging can be and how quickly it can operate. Such results will help us to understand how mating systems that involve a mixture of selfing and outcrossing evolve. They will also illuminate the genetic hazards faced by small populations and demonstrate whether intentional inbreeding can provide a useful breeding strategy for small populations in threatened or endangered species.