(A) Schematic map (not to scale) of transformation vectors pVS11, pP2-bar, and pP2-cre. Only relevant features and DNA segments are shown. Solid arrowhead, loxP; open arrowhead, lox511. P1, rice actin promoter; P2, maize ubiquitin promoter; bar, phosphinothricin acetyl transferase coding region; cre, Cre recombinase coding region; E, EcoRI; H, HindIII; P, PstI; X, XhoI. Restriction fragments that hybridize to the probes (a, b, or c) are in kilobases. Transgene–host DNA junction fragments that hybridize to probe b are indicated by dotted arrows. Not shown are the pUC18 vector backbones and the nos3′ (transcription terminator) fragments that lie immediately downstream of bar and cre. (B) Resolution product from recombination of lox sites. pVS11 may integrate in multiple copies, with the outermost copies forming four possible configurations. Recombination between the outermost lox511 sites (indicated by dashed lines) resolves the complex locus into a unit copy of pVS11. Recombination between loxP sites removes the selectable marker.