what is junk dna

Junk DNA, also known as non-functional DNA, is a DNA sequence that has no relevant biological function. Most organisms have some junk DNA in their genomes, mostly pseudogenes and fragments of transposons and viruses. The term "junk DNA" was popularized by Susumu Ohno in a 1972 paper where he concluded that 90% of mammalian genomes consisted of nonfunctional DNA. However, the phrase "junk DNA" is debatable, and differing precise definitions provide wildly disparate estimates of its prevalence. In fact, it is becoming clear that at least some of the noncoding DNA is integral to the function of cells, particularly the control of gene activity. For example, noncoding DNA contains sequences that act as regulatory elements, determining when and where genes are turned on and off. Some structural elements of chromosomes are also part of noncoding DNA, such as repeated noncoding DNA sequences at the ends of chromosomes that form telomeres, which protect the ends of chromosomes from being degraded during the copying of genetic material. In summary, while the term "junk DNA" is still used, it is becoming increasingly clear that noncoding DNA plays an important role in the function of cells and the regulation of gene activity.