long double$-$stranded RNA

class of double$-$stranded RNA molecules, $20-25$ base pairs in length, that functions in RNA silencing and post$-$transcriptional regulation of gene expression with high specificity $($only has one mRNA target$)$

small non$-$coding RNA molecule $($containing about $22$ nucleotides$)$ that functions in RNA silencing and post$-$transcriptional regulation of gene expression.

largest class of small non$-$coding RNA molecules expressed in animal cells that form RNA$-$protein complexes through interactions with piwi proteins to silence of retrotransposons and other genetic elements in germ line cells through both epigenetic and posttranscriptional mechanisms