Isolation and characterization of Df(3R)BSC750 Stacey Christensen, Kim Cook and Kevin Cook Bloomington Stock Center Indiana University Df(3R)BSC750 was isolated as a FLP recombinase-induced recombination event involving PBac{RB}CG6912e00345 and P{XP}d06581. The deletion was isolated as a chromosome lacking miniwhite markers in progeny of w1118; P{hs-hid}3, Dr1/TM6C, Sb1 cu1 females crossed to P{hsFLP}1, y1 w1118; PBac{RB}CG6912e00345/P{XP}d06581 males. The males were heat shocked as larvae as described in Parks et al., Nature Genetics 36: 288-292, 2004 (FBrf0175003). This cross and crosses in preceding and succeeding generations maintained the original genetic background of the Exelixis insertion stocks (Thibault et al., Nature Genetics 36: 283-287, 2004; FBrf0175002). The recombination event generated the genetic element P+PBac{XP5.RB3}BSC750 from the segment of PBac{RB}CG6912e00345 to the left of its FRT site and the segment of P{XP}d06581 to the right of its FRT site. Its presence was verified using the PCR methods and primers described in Parks et al. with the substitution of the primer 5'-GCTTCTAAACGCTTACGCATAAACGATG-3' for the RB3' plus or RB3' minus primer in the Hybrid PCR protocol in the Supplementary Methods. The cytological breakpoints of Df(3R)BSC750 predicted from the Release 5 genomic coordinates of the transposable element insertion sites are 88E2;88E5. Df(3R)BSC750 failed to complement tefuatm-3 and Df(3R)BSC635.