© 2010 HowStuffWorks.com
Labeling any part of our genetic makeup "junk" was tempting fate. After all, wouldn't any sane person look at the incredible complexity of human DNA and muse, "Eh, it's probably there for a reason?" But for a long time, scientists just didn't know what lay between our genes in the jungle of DNA. So "junk" it was. But let's back up and remind ourselves what all that genetic material is in the first place.
Deoxyribonucleic acid is the physical substance that contains our genes. (Each chromosome is one long string of DNA.) A typical protein-coding gene has sequences of DNA that control when the gene is expressed, along with a coding sequence that's copied (or "transcribed") to make ribonucleic acid. The RNA copy is then "translated" into a protein.
But don't get too comfortable. Only a small portion of our DNA is made up of these protein-coding genes. Some genes are transcribed into RNA that never becomes proteins, and huge chunks of our DNA are never transcribed into RNA at all.
This was pretty confusing for the scientists who first started studying the genome (aka an organism's complete package of genetic material) in the '70s. If the vast majority of our DNA isn't coding for any protein, then what the heck is it doing there? Because they couldn't answer the question, the pioneers gave that noncoding DNA the unfortunate title of "junk." And thus, "junk DNA" lives on in the lexicon instead of a more sensitive title like, "moving-to-the-beat-of-a-different-drummer DNA" or "dancing like no one's watching DNA."
Up until the first "draft" of the Human Genome Project in 2000, scientists still were pretty certain that junk DNA didn't serve an essential function. But in 2012, a group of geneticists published multiple findings that finally began showing that one person's junk is another person's treasure. Well, more like one person's junk is the same person's treasure, since the DNA previously thought to be fluff in the way of the good stuff turned out to be the very thing that told the good stuff how to be good.
Confused? Climb your double helix ladder to the next page where we'll explain more in-depth.