In 1997 Tokyo scientists at Osaka University added jellyfish genes to mice, causing the cells of the mice to glow under fluorescent light.

The mice are created using a process called zygote microinjection. In this process, the scientists took a protein from a species of fluorescent jellyfish called Aequorea Victoria. Then they modified the gene to make its glowing properties twice as powerful. This gene, called EGFG (enhanced green fluorescent gene) was then inserted into a fertilized mouse egg cell. As the cell divided, the green gene also replicated and made its way into every cell of the mouse.

This genetic trait will be passed on to the majority of their offspring. The vibrant hues of the young mice will soon disappear when hair grows over their bodies, but their feet and mouths continue to glow well into adulthood.

Professor Masaru Okabe and his team started the project in 1993 in an effort to develop new methods to observe the internal development of fetuses.

The ability to detect the presence of a gene, without having to remove tissue for biopsy or destroy the test subject for autopsy, allows researchers to decrease the number of test animals required for a study and to gather the results of the study more quickly.

Scientists also hope to be able to use light emitting genes to detect the path a virus takes when spreading through an organism, and indicate which parts of the organism are most effected.

The same processes was used by French scientists to produce a glowing rabbit (named Alba). The albino rabbit glows green when placed under special lighting.

Scientists at Standford University in the U.S. have created their own glowing mice using genes from fireflies. In fireflies, the enzyme luciferase reacts with a chemical called luciferin to generate light.

The U.S. scientists introduced the luciferase gene into the lungs of their mice. After activating the luciferase genes by injecting luciferin into the mice, the researchers were able to detect, from outside of the animal, light coming from the lungs.