Step-by-step explanation:
Non-coding DNA sequences are components of an organism's DNA that do not encode protein sequences. Some non-coding DNA is transcribed into functional non-coding RNA molecules (e.g. transfer RNA, ribosomal RNA, and regulatory RNAs). Other functions of non-coding DNA include the transcriptional and translational regulation of protein-coding sequences, scaffold attachment regions, origins of DNA replication, centromeres and telomeres. Its RNA counterpart is non-coding RNA.
The amount of non-coding DNA varies greatly among species. Often, only a small percentage of the genome is responsible for coding proteins, but an increasing percentage is being shown to have regulatory functions. When there is much non-coding DNA, a large proportion appears to have no biological function, as predicted in the 1960s. Since that time, this non-functional portion has controversially been called "junk DNA".[1]
The international Encyclopedia of DNA Elements (ENCODE) project uncovered, by direct biochemical approaches, that at least 80% of human genomic DNA has biochemical activity, which they defined as being transcribed, a definition not shared with most other biologists.[2] Though this was not necessarily unexpected due to previous decades of research discovering many functional non-coding regions,[3][4] some scientists criticized the conclusion for conflating biochemical activity with biological function.[5][6][7][8][9] Estimates for the biologically functional fraction of the human genome based on comparative genomics range between 8 and 15%.[10][11][12] However, others have argued against relying solely on estimates from comparative genomics due to its limited scope.[citation needed] Non-coding DNA has been found to be involved in epigenetic activity and complex networks of genetic interactions and is being explored in evolutionary developmental biology.[4][11][13][14]