When trying to engineer a biological device, one faces the challenge to precisely control thenumber of parts in each cell. Biology is dynamic, unlike engineering a car, where the engineersare not bothered by a control mechanism for variation in the number of wheels, biologicalcircuits change continuously. Hence, when looking in synthetic biology one is faced with thechallenge that the number of DNA or protein components from their devices will changebetween cells. Bleris et al. (2011) try to overcome this problem by using the I1-FFL motif.Through computational analysis they show that the strength of inhibition of the output by theauxiliary node affects how much I1-FFL will be able to adapt to changes in copy number.To further test their theory, they constructed synthetic circuits and then performedexperimental validations. The circuits were constructed on a single plasmid, then they use11transient transfection to insert the plasmid to the cells. The reason for use of transienttransfection is that they help generates large variability in the number of plasmids internalizedby individual cells.To test the effect of both transcriptional and post-transcriptional repression by the auxiliarynode they consider three motifs: transcriptional I1-FFL, post-transcriptional I1-FFL andtranscriptional auto-regulatory motifs. Bleris et al. (2011) revealed that the most robust, unprone to internal and external perturbations, circuit was the post-transcriptional I1-FFL , alsothey achieved the highest range of output expression. Nevertheless, all the I1-FFL have showeda level of robustness with respect to the amount of genetic template change in comparisonwith the transcriptional auto-regulatory motifs. To validate their theory that robustnessdecreases as the inhibition weakens, they mutate the circuit components.Finally, they performed an analysis on the experimental data. They revealed that the post-transcriptional I1-FFL were significantly less noisy than the other circuits. However, it is stilluncertain what the main source of the noise is.This study raises a mechanism that faces the challenge of the number of DNA or protein changebetween cells, the mechanism can obtain a robust output regardless of the variation in theamount of genetic template. The findings of this study provides much support for the idea thatpost-transcriptional IFFL may be a powerful tool for biologists (Batchelor & Lahav, 2011).The findings of this study motivated to perform further studies in the field of FFL circuits. Forexample, Kim et al. (2014) constructed a synthetic circuits based on the IFFL motif that showsexact adaptation and fold-change detection. At first they theorized mathematically andsystematically characterize a model for the circuit, they performed tests to verify underlyingmodel assumptions. Then they have measured the ability of their circuit based on the IFFL toperform exact adaptation and fold-change detection, which matched the model predictions.These results present a rational and systematic design strategy of a dynamically rich syntheticcircuit. The circuit constructed in this study can allow to better understand the architecture andthe response of cellular system to inputs for example.