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Homology: Some Genes Never Go out of Style

Months before you were born, one of your genes, called Pax-6, turned on and helped your developing body build eyes. However, we are not the only species equipped with a copy of this gene. Other mammals, birds, fish, and even insects also carry a version of Pax-6. In fact, Pax-6 seems to do about the same job in all of these species. The human version of the gene can be inserted in a fly and still trigger the building of an insect eye! This suggests that Pax-6 is an ancient gene that was present in the common ancestor of most animals on Earth today and that was inherited by descendents as distantly related as flies, humans, and hummingbirds!

Fly eye Human eye Hummingbird eye

Human eye photo courtesy of NASA/JPL-Caltech; fly eye photo courtesy of Wai Pang Chan; Hummingbird photo © 2000 Ann Cook.

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