REU: The Genetic Basis of Morphological Evolution in Maize

植物物种的形态分化与 一般都有生殖隔离和遗传差异。 外表截然不同的物种通常也具有繁殖能力 不相容的（不能制造杂交种，或者如果获得， 无菌的）。 然而，一些植物物种， 在遗传意义上是相关的， 可育的在形态上可能看起来非常不同。 这 这种情况迫使植物进化论者假设， 这些特殊的植物物种一定经历了 形态进化 他们在外表上有了很大的变化 在一段太短的时间内， 生殖隔离机制。 种植玉米是一种 这种特殊的物种，与其野生祖先相比， 墨西哥的一种玉米。 这种快速形态变化的遗传基础可能 取决于两种截然不同的模式： 具有主要影响的基因的数量（1到4个），或多个 许多基因的变化，每一个都有很小的影响。 John Doebley博士 在他的遗传学研究中， 对玉米穗部形态变化的影响 亚种玉米 玉米穗与 它的祖先，墨西哥大刍草，尽管事实上， 玉米和大刍草是完全可育的， 在一万年前的印第安人驯化下才开始分化。 试验将在玉米和大刍草之间的后代上进行 种族，分析分子标记之间的关联， 控制玉米形态特征的染色体和基因 和玉米穗。 通过这些手段， 确定控制关键基因的最小数目 玉米和大刍草之间的形态差异， 这些基因的染色体定位，作用方式（显性） 或隐性），以及表型变异的百分比， 每一个基因都有自己的账户。 数据将允许歧视 两种相互竞争的理论之间的形态步骤 与玉米穗的起源有关

Morphological differentiation in plant species is correlated in general with reproductive isolation and genetic differences. Very different-looking species are usually also reproductively incompatible (hybrids cannot be made, or if obtained, are sterile). Nevertheless, some plant species which are closely related in the genetic sense that they are completely interfertile may look very different morphologically. This situation has compelled plant evolutionists to hypothesize that these exceptional plant species must have undergone rapid morphological evolution. They have changed greatly in appearance in a period of time that was too short to allow them to evolve mechanisms of reproductive isolation. Cultivated maize is one such exceptional species, compared to its wild progenitors, the teosinte corns of Mexico. The genetic basis of such rapid morphological change may depend upon two contrasting modes: changes at a very small number (one to four) of genes with major effects, or numerous changes of many genes, each with small effects. Dr. John Doebley is beginning to test these two hypotheses in his study of genetic effects on morphological changes in the ear of corn, Zea mays subspecies mays. The ear of corn is remarkably different from that of its ancestor, Mexican teosinte, despite the fact that corn and teosinte are completely interfertile and are thought to have diverged only 10,000 years ago under Indian domestication. Tests will be conducted on progeny between corn and teosinte races, analyzing associations between molecular markers on the chromosomes and genes controlling morphological features in corn and teosinte ears. By these means it should be possible to determine the minimum number of genes controlling key morphological differences between corn and teosinte, the chromosomal location of these genes, the mode of action (dominant or recessive), and the percentage of phenotypic variation for which each gene accounts. The data will allow discrimination between two competing theories on the morphological steps involved in the recent origin of the corn ear.