Ribonucleic acid (RNA) can serve genetic, catalytic, structural, and regulatory roles. Non-coding RNA (ncRNA) genes make transcripts that function directly as RNA, rather than encoding proteins. Transfer RNA and ribosomal RNA are well known examples of non-coding RNA. Around 98% of all transcriptional output in humans is non-coding RNA. RNA-mediated gene regulation is widespread in higher eukaryotes and complex genetic phenomena like RNA interference, co-suppression, transgene silencing, imprinting, methylation, and possibly position-effect variegation and transvection, all involve intersecting pathways based on or connected to RNA signaling. Due to its high abundance, non-coding RNAs have several important biological roles in living organisms.