Targeted insertion of thymidine kinase into the C57BL/6J derived Chromosome 5 Htt locus in the v6.4 ES cell line was followed by 400 Gy of gamma radiation, FIAU selection, and injection into C57BL/7J blastocysts. The deletion includes the full Wolf-Hirschhorn syndrome critical region and extends to include D5Mit148 and Qdpr. (J:67077)