worms have been genetically modified to make them glow under ultraviolet
light. Worms don't usually glow, but some jellyfish do. The nerve
cells of these worms glow because scientists injected their parents
with the gene that makes jellyfish glow. Because the genes of living
things are so similar, the worm takes on the jellyfish characteristic.
By making the nervous system in the worms glow scientists can watch
how nerve cells communicate with each other. The glow gene is used
to trace biological processes in all sorts of organisms.