Dissertation Research: Genetic Basis of Flowering Date in Arabidopsis thaliana

植物的繁殖力和首次繁殖年龄等生活史特征与植物的最终生存和繁殖能力密切相关。生活史特征直接受到人工和自然选择的影响，因此植物育种者和进化生物学家都特别关注这一问题。这些性状的表达被认为是许多微效基因(数量性状座位或QTL)的结果。对进化变化的速度和方向的预测取决于分离QTL的数量和它们的影响的大小。涉及数量变异的QTL的实际数量，以及大效应QTL的重要性和流行率仍然几乎是未知的。基于统计理论的方法被用来估计影响一个性状的QTL的最小数目及其影响的相对大小，但这些方法缺乏精度。相比之下，分子生物学和经典数量遗传学技术提供了一种强大的手段来估计QTL的最小数量及其相对效应。本研究将利用拟南芥的遗传标记回答以下问题：1)有多少QTL控制开花时间？2)是否存在大效应基因？3)开花时间与其他对植物生存有重要影响的性状之间的相互作用是否阻止了大效应基因在开花时间进化中的重要作用？拟南芥是这项研究的理想生物，因为现有的图谱非常完整。自然产生的近交系的存在极大地简化了统计分析。这些技术已经成功地用于一些农作物的重要经济性状的标记辅助选择程序。它们是基因改良计划中的强大工具，也是解决基本进化和遗传问题的有力工具。然而，这些技术还没有应用于自然植物种群。这项工作将提供一些关于基因数量和物种内遗传效应大小的第一批数据。

Life history characters such as fecundity and age at first reproduction, are closely related to the ultimate survival and reproductive ability of plants. Life history traits are directly affected by artificial and natural selection and are therefore of particular concern for both plants breeders and evolutionary biologists alike. The expression of these traits is thought to be the result of many genes of small effect (quantitative trait loci or QTLs). Predictions about the rate and direction of evolutionary change depend on the number of segregating QTLs and the magnitude of their effects. The actual number of QTLs involved in quantitative variation, and the importance and prevalence of QTLs of large effect is still virtually unknown. Methods based on statistical theory have been used to estimate the minimum number of QTLs influencing a trait, and the relative magnitude of their effects, but these methods lack precision. In contrast, techniques of molecular biology and classical quantitative genetics provide a powerful means of estimating the minimum number of QTLs and their relative effects. This study will use genetic markers in Arabidopsis thaliana to answer the following questions: 1) How many QTLs control the timing of flowering? 2) Are there genes of large effect? 3) Do interactions between flowering time and other characters important to plant survival prevent genes of large effect from being important in the evolution of flowering time? Arabidopsis is the ideal organism for this study because the existing map is extraordinarily complete. The existence of naturally occurring inbred lines greatly simplifies statistical analyses. These techniques have been used with success in marker-aided selection programs for economically important traits in a few crop plants. They are powerful tools in genetic improvement programs, as well as for addressing fundamental evolutionary and genetic questions. However, these techniques have not been applied to natural plant populations. This work will provide some of the first data on the number of genes and the magnitude of genetic effects within species.