Are RNAi and Micro- RNAs the same?

miRNA are small "RNA molecules" which are involved in gene silencing via translational repression or target degradation whereas RNAi or RNA interference is an RNA-dependent gene silencing "process" that is controlled by the RNA-induced silencing complex (RISC) and is initiated by short double-stranded RNA molecules in a cell's cytoplasm (from wikipedia).

What I think that you want to ask the difference between miRNA and siRNA (small-interfering RNA). Well, both are involved in RNAi and function-wise both are pretty similar i.e. to stop translation or silence a gene at RNA level(either by repression or degardation of mRNA). But there're some difference between them. miRNA are endogenous, made by the cells, often transcribed from non-coding RNA (the process is quite long so check the diagram on wikipedia) and functions to silence a gene most of the times by translational repression (miRNA base pair with mRNA to form dsRNA; stop its translation) or mRNA degradation. Which mechanism to chose depends upon base pairing of miRNA with mRNA, if perfect then target mRNA is fully degraded or if its imperfect well mRNA will be just blocked. siRNA are exogenous dsRNA that is taken up by cells or enter via vectors (in simple terms its made synthetically). But what makes them different is that siRNA, most of the times, make a perfect base-pairing with target mRNA so completely degrading it. For most molecular experiments (where we want to silence some gene at RNA level) siRNA is preferred.

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