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August 16, 2005; 102 (33)
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Cover image: Sonic hedgehog gene expression (blue) in the developing feathers of an embryonic duck, showing a prepattern of branched morphology. Formation of this feather branching prepattern is controlled by activatormorphogenetic protein 2. See the article by Harris et al. on pages 11734–11739. Image courtesy of Matthew P. Harris.

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