ABOVE: TEXTBOOK EXAMPLE
In the murky darkness, blue and green blobs are dancing. Sometimes they keep decorous distances from each other, but other times they go cheek to cheek—and when that happens, other colors flare.
The video, reported last year, is fuzzy and a few seconds long, but it wowed the scientists who saw it. For the first time, they were witnessing details of an early step—long unseen, just cleverly inferred—in a central event in biology: the act of turning on a gene. Those blue and green blobs were two key bits of DNA called an enhancer and a promoter (labeled to fluoresce). When they touched, a gene powered up, as revealed by bursts of red.
The event is all-important. All the cells in our body contain by and large the same set of around 20,000 distinct genes, encoded in several billion building blocks (nucleotides) that string together in long ...
