FRT100 is an engineered recombination target site derived from the wild-type FRT site (the target site for the FLP recombinase encoded by the Saccharomyces cerevisiae 2μ plasmid). The recombination efficiency of the FRT100 site in the presence of FLP is approximately 100x less efficient than that of the wild-type FRT site, due to a point mutation in one of the two 18bp inverted repeats of the minimal FRT sequence (FBrf0251446).