Publisher's Synopsis
Spatially periodic patterns like zebra stripes or insect segments are mysteriously precise. How do they form during development? The deeper question, which lies at the heart of developmental biology, is: how do cells in different places within an embryo acquire different states of gene expression? In principle, there are three possible answers: either a cell's position causes its state, or its state causes its position, or both are caused by some third agent. These alternatives provide a framework for classifying theoretical models. Positional information models, the most widely used today, belong to the first category.;In order to facilitate comparisons, this book strips away all ad hoc assumptions to expose the central tenets of each model, traces the historical roots and familial relationships among different types of models, and illustrates the rules of each model in terms of how it would solve the same basic problem. It also re-examines the computer metaphor in developmental biology: are embryonic cells robots in disguise? The surprising answer - based upon their ability to perform Boolean logic, store and process information, execute iterative subroutines and malfunction in predictable ways - is yes.
