The Bicoid (Bcd) gradient is shallow, Bicoid concentration (y-axis) degrades over about 1/2 of total embryo length (x-axis). However, this shallow gradient provides positional information for Hunchback (Hb), which is translated as long as there are even low levels of Bicoid protein1,2. This sharp Hunchback gradient neatly splits the embryo into anterior and posterior halves. Later in development the presence of high Hb + high Bcd, high Hb, low Bcd, and low Hb + low Bcd will be read by different transcription factors to produce broad stripes in the embryo
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bicoid, hunchback, drosophila, evodevo, evolutionary developmental biology, gradient, model