选择牵连效应分析：发掘重要基因的新思路

作物在长期进化过程中，除自然选择外，还经历了两次大的人工选择，即人工驯化选择和育种选择，使栽培种与野生种之间、现代品种与古老的地方品种之间在群体遗传结构及性状上形成了很大的差异；在基因组中，一些承受强选择作用的基因在群体中的多样性显著降低，同时这些基因附近区域的遗传多样性也明显下降。在遗传学中将这种对个别基因的选择导致其侧翼区域遗传多样性降低的现象称之为选择牵连效应（Hitchhiking effect，也称选择搭载效应）。通过大群体多位点的扫描分析，可找到一些发生选择牵连效应的基因组区段，利用标记/性状关联分析（Marker/Trait association analysis），就可发现这些区段所控制的重要性状；对这些区段进行精细扫描和分析，即可找到一些决定重要农艺性状的基因，并发现优异等位变异，从而为重要基因的克隆和作物品种的分子设计奠定基础。各大作物高密度分子标记连锁图谱的绘制完成、高通量基因型分析技术体系的建立，为利用选择牵连效应分析、通过标记/性状之间的关联，寻找和定位一些重要基因奠定了基础。本文在查阅文献的基础上，结合作者的研究，以小麦株高、千粒重、磷的吸收和利用等性状为例，就选择牵连效应分析的基本思路、方法进行了讨论，以起到抛砖引玉之作用。

Hitchhiking Effect Mapping: A New Approach for Discovering Agronomic Important Genes

Beside natural selection, today's cultivated crops have experienced two types of strong artificial selections: domestication and modern breeding. Domestication has led to a giant genetic structure differentiation between cultivars and their wild relatives, and modern breeding has created further genetic structure differentiation between the modern varieties and the landraces. In a genome, genetic diversity at a locus experienced strong selection is significantly lower than that at other loci non-experienced selection and diversities in the flanking regions also declines. This phenomenon is called the hitchhiking effect or genetic selection sweep. The genomic regions with selection sweep could be detected through scanning a number of released varieties or natural populations with molecular markers. Thereafter, agronomic important traits linked with these regions could be detected using Marker/Trait association analysis. Fine scanning of these genomic regions would help to determine the sizes of these regions and to discover the favorable alleles or even the key genes. This could provide very valuable information for gene isolation and molecular design of new varieties. Establishment of high density genetic linkage maps in the major crops and availability of high throughput genotyping platform make it possible for discovering agronomic important genes through marker/trait association analysis. Based on the available publications, we give a brief introduction of the hitchhiking effect mapping approach using the plant height, 1000-grain weight, and phosphorus-deficiency tolerance as examples in wheat.