 Studies of evolutionary rates in "Drosophila" have shown that genes in the RNAi pathway are subject to strong directional selection and are among the fastest-evolving genes in the "Drosophila" genome.The RNA interference pathway is often exploited in experimental biology to study the function of genes in cell culture and "in vivo" in model organisms.Double-stranded RNA is synthesized with a sequence complementary to a gene of interest and introduced into a cell or organism, where it is recognized as exogenous genetic material and activates the RNAi pathway.