Scientists use the firefly's light-making gene to track transplanted organs in living rats.

The firefly's glow is so useful that scientists have copied its genetic code. Researchers created 'Firefly Rats' by adding the luciferase gene to their DNA. Because these rats glow under special cameras, doctors can track transplanted tissues and organs in real-time. It helps them see if a transplant is working without having to perform invasive surgery.