SPECIATION AND DOMESTICATION IN MAIZE AND ITS WILD RELATIVES - EVIDENCE FROM THE GLOBULIN-1 GENE

The grass genus Zea contains the domesticate maize and several wild ta xa indigenous to Central and South America. Here we study die genetic consequences of speciation and domestication in this soup by sampling DNA sequences from four taxa-maize (Zea mays ssp. mays), its wild prog enitor (Z. mays ssp. parviglumis), a more distant species within the g enus (Z. luxurians), and a representative of the sister genus ( Tripsa cum dactyloides). We sampled a total of 26 sequences from the glb1 loc us, which encodes a nonessential seed storage protein. Within the Zea taxa sampled, the progenitor to maize contains the most sequence diver sity. Maize contains 60% Of the level of genetic diversity of its prog enitor, and Z. luxurians contains even less diversity (32% of the leve l of diversity of Z. mays ssp. parviglumis). Sequence variation within the glb1 locus is consistent with neutral evolution in all four taxa. The glb1 data were combined with adh1 data from a previous study to m ake inferences about the population genetic histories of these taxa. C omparisons of sequence data between the two morphologically similar wi ld Zea taxa indicate that the species diverged similar to 700,000 year s ago from a common ancestor of intermediate size to their present pop ulations. Conversely, the domestication of maize was a recent event th at could have been based on a very small number of founding individual s. Maize retained a substantial proportion of the genetic variation of its progenitor through this founder event, but diverged rapidly in mo rphology.