If you’re a gene and you don’t make a messenger RNA that makes a protein, you’re useless. Or so researchers thought until they discovered genes that were once as invisible to us as the dark side of the moon. According to this central dogma in biology, there are about 26,000 genes in our cells that make up about 1 percent of our DNA. Lin and others have recently discovered that the other 99 percent—the mis-named “junk DNA”—contains different genes that produce at least 60,000 RNA molecules. These so-called piRNAs are typically 20-30 units long, compared to the 1,000 to 10,000 units in typical messenger RNA. Lin’s work is making it clear that these RNAs have a large role in regulating the genome—and some help stem cells renew themselves.