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parallelism in processing. More than this, the adaptive plan can modify and coordinate the broadcast units to form models of the environment. By implementing, within the language, the "prediction and correction" techniques for models discussed in Illustration 3.4, we can arrive at a very sophisticated adaptive plan, one which can rapidly overcome inadequacies in its representation of the environment. This approach will be elaborated in the next section. The "broadcast language" already makes it clear that there exist languages suitable both for defining arbitrary representations and for defining the operators which allow these representations to be adapted to environmental requirements. |
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4. Concerning Applications and the Use of Genetic Plans to Modify Representations |
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The broadcast language provides unusually straightforward representations for a variety of natural models. Such representation not only provides a uniform context for comparisons and rigorous study, it also makes clear the "computational" or processing power of the model and its susceptibility to adaptation. |
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The Britten-Davidson generalization (1969) of the "operon-operator" model serves well to illustrate the point. This is a model for regulation in higher cells; as such it includes many mechanisms not found in the simpler bacterial cells modeled by Jacob and Monod (1961). The model consists of four basic types of gene (see also Figure 14): |
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1. The sensor gene is activated (perhaps via intermediary molecules) by any of various agents (enzymes, hormones, metabolites) involved in inter- and intracellular control. That is, the sensor gene is a detector sensitive to the state of the cell and its environment. |
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2. The producer genes are the specific controls for the actual production of cell structures (membranes, organelles, etc.) and operating agents (enzymes, etc.). They are the output controls of the regulation procedure. |
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3. Each integrator gene is associated with a sensor gene and sends out a specific signal (molecule) to other genes when the sensor is activated. Several integrator genes may be associated with a single sensor, thus allowing the sensor to initiate a variety of signals. |
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4. The receptor gene is a link between integrator genes and producer genes. Each receptor gene is associated with a single producer gene and is sensitive to a single integrator signal. When the signal is received the producer gene is activated. A given producer gene may have several associated receptors. |
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