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Figure 9-6. Reaction-diffusion systems can generate repetitive patterns. (A) The principles of a basic model shown at sequential developmental times; the horizontal axis represents position along a layer of otherwise similar cells. Cells produce an activator, A, that catalyzes its own continued production. A diffuses across the tissue, where cells detecting it are stimulated to make A as well as a rapidly diffusing inhibitor, I. Cells whose receptors detect I inhibit their production of A. Where the concentration of A relative to I exceeds a threshold level, gene switching occurs leading to activity peaks (arrows) where structural units, like feathers, teeth, or tooth cusps form. (B) Seashells real and simulated. Courtesy H. Meinhardt. For model see (Meinhardt 1996; 2000; 2001; 2003).

Figure 9-6. Reaction-diffusion systems can generate repetitive patterns. (A) The principles of a basic model shown at sequential developmental times; the horizontal axis represents position along a layer of otherwise similar cells. Cells produce an activator, A, that catalyzes its own continued production. A diffuses across the tissue, where cells detecting it are stimulated to make A as well as a rapidly diffusing inhibitor, I. Cells whose receptors detect I inhibit their production of A. Where the concentration of A relative to I exceeds a threshold level, gene switching occurs leading to activity peaks (arrows) where structural units, like feathers, teeth, or tooth cusps form. (B) Seashells real and simulated. Courtesy H. Meinhardt. For model see (Meinhardt 1996; 2000; 2001; 2003).

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