**5. Genetic regulation of plasticity**

There is not enough data about the genes, promoters, and regulatory elements that control "invasive" or "weedy" phenotypes commonly observed in wild plant populations. However, the phenotypes provide key insights into potential gene families and signaling pathways. Adaptive phenotypes also provide evidence that plasticity responses are controlled genetically and by specific plasticity genes [6]. The accumulation of genetic modifications associated with adaptive responses can be tracked through time and are genetically controlled [6]. Two models have been proposed to explore how changes in adaptive response occur. The first model proposes that the expression of structural genes varies as the environment changes [68]. Genetic plasticity is not regulated by plasticity genes, rather by changes in gene expression of structural genes resulting in phenotypic changes or plasticity [68]. The second model proposes that specific regulatory genes, i.e., plasticity genes mediate responses for structural genes [69, 70]. The resulting change in expression of the regulatory genes in response to environmental changes is what ultimately controls the pattern of plasticity [69, 70].
