Molecular Evidence for Gene Flow among Zea Species

mong the concerns associated with the "release" of transgenic plants into the environment is the possibility that genes transformed into a crop plant by recombinant DNA methods could spread into its wild relatives. The process of concern is introgression, the transfer of genes from one population into another via hybridization and subsequent backcrossing. If these genes confer some selective advantage on the wild relatives, then they could contribute to the development of new or more troublesome weedy forms. For example, genes for disease, drought, and herbicide resistance could all produce problems by enhancing the fitness of the wild relatives. The available evidence for gene flow between crops and their relatives provides a context for beginning to make realistic assessments of the risk of introgression of engineered genes into wild crop relatives. In this article, I review the evidence for gene flow between maize and its nearest wild relatives, the teosintes. Because these plants are relatively well-studied, the evidence for gene flow between them can provide insight into the potential for the transfer of engineered genes from crops to their wild relatives. However, it is important to note that conclusions drawn from maize and teosinte may not be applicable to all other crop-