129-derived mESC lines tend to be stable when cultured under classical conditions in medium containing DMEM, FBS, and LIF. 129-derived lines are often the workhorse of the gene targeting laboratory and have been used to make literally thousands of mouse knockouts.

In recent years, however, there has been growing interest in producing mouse models in the C57BL/6 (B6)-derived ESC lines, thus avoiding the lengthy and expensive backcrossing into the B6 strain, which is preferred for some physiological studies.

Primogenix PRX-129/X1 Mouse embryonic stem cells have been derived from the inner cell mass of a 129/X1 blastocyst stage embryo. They are karyotypically normal male: 40XY, IMPACT tested (pathogen free), and germline competent. Germline chimeras obtained when 8-10 cells injected into b6 mouse blastocysts.

Primogenix PRX-B6N Mouse embryonic stem cells are derived from the inner cell mass of a C57BL/6N blastocyst stage embryo. They are karyotypically normal male: 40 XY, IMPACT tested, and germline competent. Germline chimeras obtained when 10-14 cells are injected into BALB/c, C57BL/6, or C57BL/6 tyr2cJ blastocysts.