Fireflies don't have a single "glow gene", but rather a complex system of genes that work together to produce their bioluminescence. The key player in this process is the luciferase gene, which encodes the enzyme luciferase.

Here's how it works:

1. Luciferase is an enzyme that catalyzes a chemical reaction involving luciferin, a light-emitting molecule.

2. Luciferin is a substrate that, when combined with oxygen and energy from ATP, gets excited by the luciferase enzyme.

3. This excited state is unstable and the molecule quickly releases energy in the form of light, creating the characteristic glow.

While the luciferase gene is crucial, other genes play supporting roles, affecting factors like the intensity and color of the light emitted.

Interestingly, different firefly species have variations in their luciferase genes, leading to distinct light colors and flashing patterns. This is why fireflies communicate using specific light signals.