Evolutionary model for the origin of the aromatase gene family. Symbols from the two conserved DNA blocks from figure 2. Dotted line boxes denote conservation of synteny but not gene order. Black bars denote "en bloc" (or genome) duplications. Star indicates tandem duplication of TMOD2/3. Horizontal curve arrow indicates gene inversion of the DNA block containing TMOD3, TMOD2, PPBP and SCGIII.