A 5' loxP site was inserted upstream of the CpG island (CGI) of interest and replaced 72 bp of endogenous DNA (mm9, chr13:48,642,634-48,642,705). A rox-flanked STOP/selection cassette with a 3' FRT and loxP sites replaced 14 bp of genomic DNA (mm9, chr13:48,640,254-48,640,267). (J:277622)