Noncoding DNA

In genetics, non-coding DNA describes DNA which does not contain instructions for making proteins (or other cell products such as noncoding RNAs). In eukaryotes, a large percentage of many organisms' total genome sizes is comprised of noncoding DNA (a puzzle known as the "C-value enigma"). Some noncoding DNA is involved in regulating the activity of coding regions. However, much of this DNA has no known function and is sometimes referred to as "junk DNA".

Recent evidence suggests that "junk DNA" may in fact be employed by proteins created from coding DNA. An experiment concerning the relationship between introns and coded proteins provided evidence for a theory that "junk DNA" is just as important as coding DNA. This experiment consisted of damaging a portion of noncoding DNA in a plant which resulted in a significant change in the leaf structure because structural proteins depended on information contained in introns.

Some non-coding DNA can be a non phenotypical RNA virus historical relic.