The human AB775805 YAC was modified with the insertion into the 3'UTR of the HBB locus control region a loxP5171 and loxP2272-flanked, inverted copy of a CpG-rich 2.3 kb lambda bacteriophage DNA fragment with four CTCF-binding sites and fragment b (LCb) sequences from the H19 imprinting control region (ICR; Rr27). (J:202262)