Isolation and characterization of Df(2R)BSC266 Stacey Christensen, Kim Cook and Kevin Cook Bloomington Stock Center Indiana University Df(2R)BSC266 was isolated as a FLP recombinase-induced recombination event involving PBac{WH}Heyf06656 and P{XP}d08527. The deletion was isolated as a chromosome lacking miniwhite markers in progeny of P{hsFLP}1, y1 w1118; PBac{WH}Heyf06656/P{XP}d08527 males crossed to w1118; P{hs-hid}2, wgSp-1/CyO females. These 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.WH5}BSC266 from the segment of PBac{WH}Heyf06656 to the left of its FRT site and the segment of P{XP}d08527 to the right of its FRT site. Its presence was verified using the PCR methods and primers described in Parks et al. Exelixis, Inc. determined the insertion site of P{XP}d08527 to be Release 3 genomic coordinate 3523385 on chromosome arm 2R. This corresponds to 44D1 on the Release 3 and Release 5 genome maps. The predicted position of PBac{WH}Heyf06656 on the Release 5 map is 44A2. Consequently, the cytological breakpoints of Df(2R)BSC266 are predicted to be 44A2;44D1. It failed to complement cul-4KG02900, Pabp2KG02359 and pnutXP.