positional info

One way of explaining regulation is to think of cells being able to obtain positional information as to where they are and to use that information in development. This way, cells can be moved about and interchanged (in experiments or accidents) without disturbing the developmental process. Gradient fields could be one source of positional information. (see also morphic fields) For Lewis Wolpert, "positional information is about graded properties" measured with reference to a "coordinate system." Wolpert's simple "French flag" model appealed to the "non-mathematical but theoretically minded." A gradient described as a straight inclined line, could have threshold points translating into patterns (eg red, white, and blue). But "just what moves this answer beyond the realm of tautology remains obscure." Evelyn Fox Keller

A "fate map" specifies the the positions of cells which give rise to different parts of the adult. (Kauffman discusses fate maps in Origins of Order. He points out that while a fate map shows that cells in a specific area will ultimately give rise to specific parts of the adult, it does not demonstrate that the cells in the blastoderm have become committed in any sense to that prospective fate. p 579) In general, cells develop early on in relation to their position, but with time their fate becomes fixed. Graftings that did not disrupt the early development become no longer possible. This process is known as determination. 

One of the primary conceptual problems of development is that these fields themselves develop, but they form in "typical" ways in the formation of embryos of distinct species. Should they be thought of as "potentialities," already inherent?