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From Fins to Wings
NOVEMBER 2006
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Photo caption by Jennifer Holland
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From Fins to Wings Gallery Photo

Genus Saimiri


Squirrel Monkey
Photograph by Rosamond Purcell

In most animals, like this squirrel monkey, Hox genes switch on early in the development of the embryo. Like a mapmaker's grid, the genes divide the blob-like embryo into compartments where specialized structures—ribs, vertebrae, limbs, eyes, the head—later take shape. "The monkey has a typical vertebrate body plan, with the addition of the long tail," says biologist Sean Carroll.


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