"Junk DNA" is what biologists used to call heterochromatin, the highly repetitive, gene-poor DNA concentrated near the centromeres and telomeres of chromosomes. With the publication of version 5.1 of the genome of the fruit fly, Drosophila melanogaster, led by scientists at Lawrence Berkeley National Laboratory and their colleagues, the term "junk" will be heard less often. Heterochromatin, it appears, is crucial to genome maintenance and cell biology.