So there’s this protein called GFP, which stands for green florescent protein that microbiologists can isolate. Once there’s enough of them on a host site (Chinese hamster ovaries, for example) their glow provides scientists with a look at how metastasis (cancer!) occurs so we can track treatments to ensure they’re working.
"In this latest bit of research, published in Nature Methods, the Mayo Clinic scientists inserted a version of the GFP gene along with a gene from the rhesus macaque that blocks the feline immunodeficiency virus (FIV)—the virus that causes feline AIDS—into the unfertilized eggs of a cat. After those eggs were fertilized, they produced kitties that glowed green, showing that they also had the anti-FIV gene. Even better, subsequent generations of cats also glowed and had the anti-FIV gene.”