The Science of Gene Flow in Agriculture and Its Role in Coexistence

Gene flow is a natural process that occurs among sexually-compatible individuals in which cross pollination can result in viable seeds. Gene flow between individuals within and among populations via pollen occurs only when they have concurrent geography, overlapping flowering times, and share common pollinators. Given a population size sufficient to avoid genetic drift, alleles that have neither positive nor negative impact on fitness will persist in the population at an allelic frequency equal to their introduction level. Alleles for genes conferring a fitness effect will be selected naturally for or against depending on the selection pressure. For example, the frequency of alleles conferring disease resistance may increase in the population in generations where a certain pathogen is prevalent but not when it is absent, while alleles conferring herbicide resistance will neither increase nor decrease in the population in areas where the herbicide is not used. Favorable genotypes for a certain trait are usually fixed at a more rapid rate in self-pollinating than in outcrossing species. Genetic and biological features such as polyploidy, fecundity, and generation time also affect shifts in allele frequencies.