ABSTRACT
This chapter considers mechanisms that can generate precise long-range patterns that are robust to genetic and environmental perturbations, following the work of Naama Barkai and her colleagues. It shows that the combination of diffusion and degradation leads to an exponentially decaying spatial morphogen profile, which varies strongly if the source strength is varied. The chapter deals with the biochemical interactions in a small network of several proteins that participate in patterning one of the spatial axes in the early embryo of the fruit fly Drosophila. These biochemical interactions can, in principle, give rise to a large family of possible patterning mechanisms. Patterning by morphogen gradients is achieved by diffusing molecules sensed by biochemical circuitry, raising the question of the sensitivity of the patterns to variations in biochemical parameters. A range of experiments has shown that patterning in development is robust with respect to a broad variety of genetic and environmental perturbations.
