Non-coding region

In genomics and related disciplines, noncoding DNA sequences are components of an organism's DNA that do not encode protein sequences. Some noncoding DNA is transcribed into functional non-coding RNA molecules (e.g. transfer RNA, ribosomal RNA, and regulatory RNAs). Other functions of noncoding DNA include the transcriptional and translational regulation of protein-coding sequences, scaffold attachment regions, origins of DNA replication, centromeres and telomeres.

The amount of noncoding DNA varies greatly among species. Where only a small percentage of the genome is responsible for coding proteins, the percentage of the genome performing regulatory functions is growing. When there is much non-coding DNA, a large proportion appears to have no biological function for the organism, as theoretically predicted in the 1960s. Since that time, this non-functional portion has often been referred to as "junk DNA", a term that has elicited strong responses over the years.

The international Encyclopedia of DNA Elements (ENCODE) project uncovered, by direct biochemical approaches, that at least 80% of human genomic DNA has biochemical activity. Though this was not necessarily unexpected due to previous decades of research discovering many functional noncoding regions, some scientists criticized the conclusion for conflating biochemical activity with biological function. Estimates for the biologically functional fraction of our genome based on comparative genomics range between 8 and 15%. However, others have argued against relying solely on estimates from comparative genomics due to its limited scope because non-coding DNA has been found to be involved in epigenetic activity and complex networks of genetic interactions, being explored in evolutionary developmental biology.

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