Courtesy of Princeton University physicists William Bialek and Thomas Gregor.

This 2-hour-old fly embryo already has a blueprint for its formation, and the process for following it is so precise that the difference of just a few key molecules can change the plans. Here, blue marks a high concentration of a key signaling protein that directs the formation of the fly's head. It also regulates another important protein (green) that further maps the head and thorax structures and partitions the embryo in half (red is DNA). The yellow dots overlaying the embryo plot the concentration of the "blue" versus "green" proteins within each nucleus. Courtesy of Princeton University physicists William Bialek and Thomas Gregor.

Featured in the April 15, 2009, issue of Biomedical Beat.
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