Campbell Biology 11th Edition by Lisa Urry,Michael Cain,Steven Wasserman,Peter Minorsky,Jane Reece

Exercise 10

The flashlight fish has an organ under its eye that emits light, which serves to startle predators and attract prey, and allows the fish to communicate with other fish. Some species can rotate the organ inside and then out, so the light appears to flash on and off. The light is not actually emitted by the fish itself, however, but by bacteria that live in the organ in a mutualistic relationship with the fish. (While providing light for the fish, the bacteria receive nutrients from the fish and in fact are unable to survive anywhere else.) The bacteria must multiply until they reach a certain density in the organ (a "quorum"; see Concept 11.1), at which point they all begin emitting light at the same time. There is a group of six or so genes, called lux genes, whose gene products are necessary for light formation. Given that these bacterial genes are regulated together, propose a hypothesis for how the genes are organized and regulated.