transgenic mouse lines: a neuronal Wnt1::Flp fusion line and a line that possessed the FRT cassette flanking the 18th exon of tm1Cwr. The authors chose this exon for excision because if it is excised, its results in a null phenotype. The authors mated the two lines and allowed the progeny to reach adulthood before the progeny were sacrificed. RNA extraction was performed on neuronal, muscular, enteric, and tail tissue. Reverse-transcription PCR and northern blotting confirmed the excision of the 18th exon of tm1Cwr abundantly in the brain tissue and moderately in muscular tissue (due to Scwhann cells within the muscle). As expected, excision was not seen in other tissues. The authors saw equal, if not better, efficiency of the FLP recombinase in cell-fate determination than Cre recombinase. In Drosophila melanogaster (Fruit Fly) To date, Flp recombinase has been utilized many times in D. melanogaster. A comparison of Flp recombinase to Cre recombinase in D. melanogaster was published by Frickenhaus et al. (2015). The authors of Frickenhaus et al. (2015) had a two-fold objective: characterize and compare the efficacy of Flp recombinase "knock-out" to Cre recombinase "knock-out" and RNAi knockdown and reveal the function of cabeza (caz), the fly ortholog to FUS, in the neurons and muscle tissue of D. melanogaster. FUS has been strongly implicated in amyotrophic lateral sclerosis (ALS) and frontotemporal dementia in humans . The authors used an elav-Gal4/UAS-Flp or Cre system to express the recombinase specifically in neurons and a Mef2-Gal4/UAS-Flp or Cre system to express it specifically in muscles. The authors conclude that the Flp recombinase "knock-out" tool is more effective than both RNAi and Cre recombinase for the purpose of knocking out specific genes in specific tissues or cell lines due to the lack of the leaky expression seen in both the Cre protein and the RNAi transcript. Also, the authors witnessed a toxicity to the Cre protein that is not seen with the Flp protein. In Danio rerio (Zebrafish) The efficacy of the FLPe recombinase system was evaluated in zebrafish by Wong et al. (2009). Embryos, that were hemizygous for a FRT-flanked enhanced green fluorescent protein (EGFP) downstream of a muscle-specific promoter, were injected with the FLPe protein. Without FLPe, these embryoes should express EGFP in all muscle tissue, and if crossed with a wild type strand, 50% of the resulting progeny should also express EGFP in muscle tissue. Embryoes, injected with FLPe, had