This transgenic strain expresses a variant of the Saccharomyces cerevisiae FLP1 recombinase gene under the direction of the human ACTB promoter. The FLPe recombinase variant exhibits enhanced thermostability with recombination activity being four-fold and ten-fold that of wildtype FLP at 37oC and 40oC, respectively. Mice that are hemizygous or homozygous for the transgenic allele are viable and fertile. Recombinase activity is detected in a wide variety of tissues (spinal cord, heart, gonad, adrenal) as early as embryonic day 10.5. This deleter strain is a suitable alternative to, and complement with the Cre-loxP system for in vivo genetic engineering. In an attempt to offer alleles on well-characterized or multiple genetic backgrounds, alleles are frequently moved to a genetic background different from that on which an allele was first characterized. It should be noted that the phenotype could vary from that originally described. We will modify the strain description if necessary as published results become available. The Jackson Laboratory 2024, used with permission.