This transgene expresses Cre recombinase under the control of a mouse Sox2 promoter contained in 12.5 kb of upstream DNA. Expression of this transgene is sex-dependent, with increased efficiency when passed through the female germline. When the transgene is passed through the male germline, cre activity is observed in epiblast cells as early as E6.5 of only those embryos that inherit the transgene and no expression is detected in extraembryonic tissue. When the transgene is passed through the female germline, cre activity is observed throughout the embryo (including the yolk sac) in all early embryos regardless of whether or not they inherit the transgene. Line 1 inserted into an intron of the gene at 89311726-89311727 (Build GRCm38/mm10) resulting in a functional knockout of the gene. Founder line 1 has a copy number of 2-5.