The fact that these homeotic genes determine an organ's identity becomes evident when a gene that represents a particular function, for example the A gene, is not expressed. In "Arabidopsis" this loss results in a flower which is composed of one verticil of carpels, another containing stamens and another of carpels. This method for studying gene function uses reverse genetics techniques to produce transgenic plants that contain a mechanism for gene silencing through RNA interference. In other studies, using forward genetics techniques such as genetic mapping, it is the analysis of the phenotypes of flowers with structural anomalies that leads to the cloning of the gene of interest. The flowers may possess a non-functional or over expressed allele for the gene being studied.