Objective    To generate chimeras for hypoxia inducible factor-1α (HIF-1α) conditional knockout mice using Cre/loxP system.     Methods    The mouse ES cells were electroporated with conditional knockout vector of HIF-1α

selected by G418-positive and Ganciclovir-negative culture. Target ES cells

following positive and negative selection

was identified by Southern blotting. Chimera mice were born by pseudopregenant mice which were transplanted with blastocysts microinjected with target ES cells.     Results    A total of 490 ES clones were collected after screening by both G418-positive and Ganciclovir-negative selection

and one clone with correct homologous recombinant event was obtained by Southern blotting screening. Five chimeras were produced following blastocysts microinjection and transplantation.     Conclusion    Chimera mice with HIF-1α conditional knockout allele were obtained

which will help to finally obtain HIF-1α conditional knockout mice

subsequently provide the possibility to study HIF-1α function in vivo.