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===Anterior - Posterior Patterning===
===Anterior - Posterior Patterning===
−
*Important in producing the correct number of digits that are of the correct morphology.
+
*Important in producing the correct number of digits of the correct morphology.
*An area of mesenchyme exists adjacent to the AER, in the posterior of the distal limb called the '''zone of polarising activity (ZPA)'''.
*An area of mesenchyme exists adjacent to the AER, in the posterior of the distal limb called the '''zone of polarising activity (ZPA)'''.
*The ZPA produces a '''morphogen'''(substance that induces other cells to change).
*The ZPA produces a '''morphogen'''(substance that induces other cells to change).