 However, the utility of these screens and the ability of techniques developed on model organisms to generalize to even closely related species has been questioned, for example from "C. elegans" to related parasitic nematodes.Functional genomics using RNAi is a particularly attractive technique for genomic mapping and annotation in plants because many plants are polyploid, which presents substantial challenges for more traditional genetic engineering methods.For example, RNAi has been successfully used for functional genomics studies in bread wheat (which is hexaploid) as well as more common plant model systems "Arabidopsis" and maize.