Abstract

A morphogen gradient is an important concept in developmental biology, because it describes a mechanism by which the emission of a signal from one part of an embryo can determine the location, differentiation and fate of many surrounding cells. The value of this idea has been clear for over half a century, but only recently have experimental systems and methods of analysis progressed to the point where we begin to understand how a cell can sense and respond to tiny changes in minute concentrations of extracellular signalling factors.

1. Wellcome/CRC Institute, Tennis Court Road, Cambridge CB2 1QR, UK, and Department of Zoology, University of Cambridge, Cambridge, UK

Correspondence to: J. B. Gurdon Correspondence should be addressed to J.B.G. (e-mail: Email: j.gurdon@welc.cam.ac.uk).