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Facilitator QuestionsBiological noise plays an important role in stochastic cell fate decisions. Define noise and speculate as to the potential sources of noise. Although noise is usually involved in stochastic cell fate decisions, it is not sufficient. Why not, and what else is required? The gene that encodes the Green Fluorescent Protein (GFP) is often used as a reporter gene given that it can be easily observed by fluorescence microscopy. As seen in this lecture, GFP is a popular reporter gene in studies of stochastic cell fate. Another gene called lacZ, which encodes an enzyme called ?-galactosidase, is also a well-known reporter gene. ?-galactosidase can be easily quantified in cell extracts by enzyme assays. Why is lacZ NOT an ideal reporter gene for studies of stochasticity in cell fate? As discussed in the lecture, a positive feedback loop is one mechanism by which small fluctuations caused by noise can be amplified. A second mechanism seen in nature involves a pair of mutually repressing repressors: Repressor 1 (R1) represses transcription of the gene encoding Repressor 2 (R2) and vice versa. Think through this circuit and explain how it would amplify a small change in the level of R1 or R2 due to noise. What is the possible advantage of stochasticity in the choice of olfactory receptors in the mouse? |
