Junk DNA: Noncoding regions of DNA that have no apparent function.
The term “junk DNA” is a disparaging one, expressing some of the disappointment felt by geneticists when they first gazed upon sizable segments of the genetic code and, instead of seeing one wonderful gene after another, they saw a few exons surrounded by vast stretches of “junk DNA.”
Exons are the regions of DNA that contain the code for producing the polypeptide molecules that make up protein. Each exon codes for a specific portion of the complete protein. In humans and some other species, the exons are separated by long regions of junk DNA.
However, junk DNA has been found to be even more conserved than protein-coding regions of the DNA in humans and other mammalian species. The extent of conservation indicates that there is some function for junk DNA that remains to be determined. Junk DNA may prove not to be junk.
I am not an expert in this, but I was always disturbed by the term “junk DNA.” We are only just beginning to understand DNA. It seems presumptous to call a sequence “junk” just because you don’t see its function. To determine that something is useless you first have to know that which is useful. Are the spaces between these words something useful or are they useless? Would someone who was never exposed to reading and writing understand the usefulness of empty spaces between words? Or would the spaces be seen as useless “junk?”