Cells’ Perception of Position in a Concentration Gradient

Wellcome CRC Institute source of the signal. Tennis Court Road To prove that a signal functions as a morphogen, it Cambridge CB2 1QR must be demonstrated that: (1) cells respond directly to and Departments of Zoology and Genetics the extracellular signaling molecule in question, and (2) University of Cambridge the cells display at least two qualitatively different Cambridge responses, apart from the nil response, at different conUnited Kingdom centrations of the signal. In most examples of concen-