Paterson A H, DeVerna J W, Lanini B, Tanksley S D
Department of Plant Breeding and Biometry, Cornell University, Ithaca, New York 14853.
Genetics. 1990 Mar;124(3):735-42. doi: 10.1093/genetics/124.3.735.
Quantitative trait loci (QTLs) have been mapped to small intervals along the chromosomes of tomato (Lycopersicon esculentum), by a method we call substitution mapping. The size of the interval to which a QTL can be mapped is determined primarily by the number and spacing of previously mapped genetic markers in the region surrounding the QTL. We demonstrate the method using tomato genotypes carrying chromosomal segments from Lycopersicon chmielewskii, a wild relative of tomato with high soluble solids concentration but small fruit and low yield. Different L. chmielewskii chromosomal segments carrying a common restriction fragment length polymorphism were identified, and their regions of overlap determined using all available genetic markers. The effect of these chromosomal segments on soluble solids concentration, fruit mass, yield, and pH, was determined in the field. Many overlapping chromosomal segments had very different phenotypic effects, indicating QTLs affecting the phenotype(s) to lie in intervals of as little as 3 cM by which the segments differed. Some associations between different traits were attributed to close linkage between two or more QTLs, rather than pleiotropic effects of a single QTL: in such cases, recombination should separate desirable QTLs from genes with undesirable effects. The prominence of such trait associations in wide crosses appears partly due to infrequent reciprocal recombination between heterozygous chromosomal segments flanked by homozygous regions. Substitution mapping is particularly applicable to gene introgression from wild to domestic species, and generally useful in narrowing the gap between linkage mapping and physical mapping of QTLs.
我们采用一种称为代换作图的方法，已将数量性状基因座（QTL）定位到番茄（Lycopersicon esculentum）染色体上的小间隔区域。QTL能够定位到的间隔大小主要由QTL周围区域中先前定位的遗传标记的数量和间距决定。我们利用携带来自奇米列夫斯基番茄（Lycopersicon chmielewskii）染色体片段的番茄基因型来演示该方法，奇米列夫斯基番茄是番茄的野生近缘种，其可溶性固形物含量高，但果实小且产量低。鉴定了携带常见限制性片段长度多态性的不同奇米列夫斯基番茄染色体片段，并使用所有可用的遗传标记确定了它们的重叠区域。在田间测定了这些染色体片段对可溶性固形物含量、果实重量、产量和pH值的影响。许多重叠的染色体片段具有非常不同的表型效应，表明影响表型的QTL位于片段差异仅为3厘摩的间隔区域内。不同性状之间的一些关联归因于两个或多个QTL的紧密连锁，而非单个QTL的多效性效应：在这种情况下，重组应能将理想的QTL与具有不良效应的基因分开。这种性状关联在远缘杂交中的突出表现似乎部分是由于纯合区域侧翼的杂合染色体片段之间的相互重组频率较低。代换作图特别适用于从野生种向栽培种的基因渐渗，并且通常有助于缩小QTL的连锁作图与物理作图之间的差距。
