 Organisms vary in their ability to take up foreign dsRNA and use it in the RNAi pathway . The effects of RNA interference can be both systemic and heritable in plants and C. elegans , although not in Drosophila or mammals . In plants , RNAi is thought to propagate by the transfer of siRNAs between cells through <unk> ( channels in the cell walls that enable communication and transport ) . <unk> comes from methylation of promoters targeted by RNAi ; the new methylation pattern is copied in each new generation of the cell . A broad general distinction between plants and animals lies in the targeting of endogenously produced miRNAs ; in plants , miRNAs are usually perfectly or nearly perfectly complementary to their target genes and induce direct mRNA cleavage by RISC , while animals ' miRNAs tend to be more divergent in sequence and induce translational repression . This translational effect may be produced by inhibiting the interactions of translation initiation factors with the messenger RNA 's <unk> tail . 
