Kingdom of Cages by Sarah Zettel

Humanity has spread among the stars, colonizing new worlds. Now the species is in danger of extinction from the interrelated disasters of virulent new diseases and collapsing ecosystems. Of all the colony worlds, only Pandora is unaffected, and the Pandorans are fanatically determined to preserve both their health and the pristine ecosystem, which they keep off-limits even to themselves. But the colonies have vowed to destroy Pandora if its biogenetics experts don't find a cure for the "diversity crisis." The Pandorans struggle without hope until they discover something in the Trust family genes that might save the devastated colonies. And two innocent girls, Chena and Teal Trust, find themselves fugitives in the narrow, closed settlements of Pandora, pursued by desperate scientists and criminals who will do anything, even commit murder, to gain control of the girls' genes.