Abstract Gene duplication and divergence are overwhelmingly
considered to be the primary mechanisms by
which cytochrome P450 monooxygenases (P450s) have
radiated into a large and diverse gene superfamily. To address
how environmental stress drives the fixation and diversification
of gene duplications, we have analyzed Cyp12d1 and
Cyp12d3, a pair of duplicated genes found in the sequenced
Drosophila genomes of the melanogaster group. The paralog
Cyp12d3, which is not found in Drosophila melanogaster, is
basal to the melanogaster group, after it split fromthe obscura
group (ca. 50 mya), and has a significant signature of positive
selection in two species (D. sechellia and D. ananassae).