Junk DNA

Junk DNA (non-functional DNA) is a DNA sequence that has no relevant biological function.^[1][2] Most organisms have some junk DNA in their genomes—mostly pseudogenes and fragments of transposons and viruses—but it is possible that some organisms have substantial amounts of junk DNA.^[3]

All protein-coding regions of genes are generally considered as functional elements in genomes. Additionally, non-protein coding regions such as genes for ribosomal RNA and transfer RNA, regulatory sequences controlling expression of those genes, elements of the genome involving origins of replication (in all species), centromeres, telomeres, and scaffold attachment regions (in eukaryotes) are generally considered as functional elements of genomes as well. (See Non-coding DNA for more information.)

It is difficult to determine whether other regions of the genome are functional or nonfunctional. There is considerable controversy over which criteria should be used to identify function. Many scientists have an evolutionary view of the genome and they prefer criteria based on whether DNA sequences are preserved by natural selection.^[4][5][6] Other scientists dispute this view or have different interpretations of the data.^[7][8][9]