| The genetic architecture of the evolution of extreme morphological divergence is one of the fundamental questions of evolutionary biology. Maize ( Zea Mays ssp. mays) and its wild ancestor, teosinte (Zea mays ssp. parviglumis) provide an ideal model for examining this question in part because of their extreme phenotypic divergence in plant architecture, ear morphology, and environmental range. In order to examine the genetic changes underlying this divergence, we use a population of maize-teosinte BC2S 3 RILs. Using these RILs allows us to examine genetic architecture on multiple levels. First, whole genome QTL mapping is used to explore the diversity of genetic architectures which control domestication traits. These genetic architectures range from nearly Mendelian to polygenic. For two near Mendelian traits, glume architecture and barren ear base, the largest QTL contained a single gene in the 1.5 LOD confidence interval. The most polygenic trait was ear diameter, for which we found 35 QTL of varying effect sizes. As part of this project we extended the capabilities of the statistical program R/qtl to apply to a wider variety of experimental crosses. In order to examine the causes of extreme morphological divergence on the single gene level, we fine-mapped a single gene, ZmCCT which controls an approximately 9 day difference in flowering time between the homozygous maize and teosinte classes. We demonstrate that the causative difference is cis-regulatory, as under long day lengths ZmCCT alleles from diverse teosintes were consistently expressed at a higher level than the corresponding temperate maize alleles. Taken together these results provide examples of the variety of ways in which complex traits evolve. |
