Steitz later discovered another kind of snRNP particle, the snoRNP, involved in an important minority of mRNA splicing reactions. Via analysis of the genetic locations of the genes for snoRNPs, she demonstrated conclusively that introns are not "junk DNA" as they had often been described. Her work helps explain the phenomenon of "alternative RNA splicing." Her discovery of the snRNPs and snoRNPs explains a mysterious finding: humans have only double the number of genes of a fruit fly. "The reason we can get away with so few genes is that when you have these bits of nonsense, you can splice them out in different ways," she said. "Sometimes you can get rid of things and add things because of this splicing process so that each gene has slightly different protein products that can do slightly different things. So it multiplies up the information content in each of our genes."