- segments of DNA that have no apparent genetic function.
- DNA that consists of repeated sequences of nucleotide and has no apparent function
- DNA that serves no known biological purpose, such as coding for proteins or their regulation. Junk DNA makes up the vast majority of the DNA in the cells of most plants and animals, composing, for example, about 95 percent of the human genome.
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.