The Df(h1q21)/+ mouse line was developed for H. Lundbeck A/S, by Taconic Biosciences GmbH (Cologne, Germany), by deletion of the human h1q21.1 orthologous genomic region on mouse chromosome 3. Two targeting vectors were generated using bacterial artificial chromosome clones from the C57BL/6J RPCI-23 library and transfected into TaconicArtemis C57BL/6N Tac embryonic stem cell line. The first vector introduced a loxP site upstream of the Gpr89 gene. The second vector introduced a loxP site downstream of the Prkab2 gene. Homologous recombinant clones were isolated and the 0.8 megabase region on mouse chromosome 3 between the loxP sites was removed using in vitro Cre-mediated recombination. Hemizygotic embryonic stem cells were injected into blastocysts isolated from impregnated BALB/c female mice and transferred to pseudopregnant NMRI female mice. Chimeric male pups were selected by coat color and mated with wild-type C57BL/6 female mice. Finally, a chimera with germline transmission was selected for expansion breeding.  The colony was maintained by mating wild-type C57BL/6N mice with hemizygous Df(h1q21)/+ mice.