GGTC records currently say that TBV2 ES cells were used to generate this allele. However information submitted to the NCBI Genome Survey Sequences Database (dbGSS) by the German Genetrap Consortium (GGTC) for gene trap cell line W056E05 gives R1 as the ES cell line used to create this allele. The original publication reporting large scale production of gene trap clones using four gene trap vectors says that ES cell-derived chimeras were produced using three ES cell lines (E14.1 (129P2/OlaHsd), R1 ((129X1/SvJ x 129S1/Sv)F1-Kitl+), TBV2 (129S2/SvPas)). Chimeric mice were subsquently bred to C57BL/6 females.