Generation of C57BL/6 knockout mice using C3H x BALB/c blastocysts.

The International Mouse Knockout Consortium aims to generate a knockout mouse for every single gene on a C57BL/6 background. Our ability to generate such mice is hampered by the poor economics of producing blastocysts to achieve germline transmission of C57BL/6 embryonic stem (ES) cells. We demonstrate superior utility of (C3H x BALB/c)F1 blastocysts compared with BALB/c blastocysts, with blastocyst numbers and germline transmission from subsequent chimeras at a rate 2- to 3-fold higher than that produced with BALB/c blastocysts.