National Geographic News recently did a spot on the many animals that glow due to being genetically modified as well as some that have naturally occurring glow.
Each featured specimen is a different type of animal and their reasons for glowing all differ as well. For example, the mice in the first photo of the gallery glow because of "green fluorescent protein, received via DNA from father, which had been implanted with glowing sperm-creating cells from a flourescent mouse."
For more complete about each specific genetically glowing animal, be sure to read the article on National Geographic.
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