 Most functional genomics applications of RNAi in animals have used C. elegans and Drosophila , as these are the common model organisms in which RNAi is most effective . C. elegans is particularly useful for RNAi research for two reasons : firstly , the effects of gene silencing are generally heritable , and secondly because delivery of the dsRNA is extremely simple . Through a mechanism whose details are poorly understood , bacteria such as E. coli that carry the desired dsRNA can be fed to the worms and will transfer their RNA payload to the worm via the intestinal tract . This " delivery by feeding " is just as effective at inducing gene silencing as more costly and time @-@ consuming delivery methods , such as soaking the worms in dsRNA solution and injecting dsRNA into the gonads . Although delivery is more difficult in most other organisms , efforts are also underway to undertake large @-@ scale genomic screening applications in cell culture with mammalian cells . 
