junk DNA

n.
DNA that does not code for proteins or their regulation but constitutes approximately 95 percent of the human genome. It is postulated to be involved in the evolution of new genes and possibly in gene repair.

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The noncoding portions of the genome were formerly referred to as "junk" DNA. Some of this material turns out to play regulatory roles in DNA replication and transcription, and the rest may be an evolutionary holdover.

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Segments of DNA along a chromosome that are not genes, do not code for anything that we know of, and whose purpose we do not understand. Approximately ninety-five percent of the human genome falls into this category. The term junk may be misleading, however, as this DNA may have other functions, such as regulating genes during development.

Some scientists speculate that junk DNA may be archaic material left over from an earlier stage of evolutionary development.