The Biological Foundations of Animal Patterns

Abstract

Pattern formation in morphogenesis has been a subject of considerable investigation by amny biologists working in diverse fields. The present article takes into account various lines of inquiry on the genesis of regular patterns in terms of concepts of genetics, embryology, biophysics, biochemistry, and mathematics and attempts to determine their contribution to the emergence of a general concept. The main emphasis is laid on primary patterns from which the final patterns are derived. The development of a pattern can be brought about by two processes, one concerned with the formation of a "prepattern" which determines the positions at which structures are formed and the other determining the amount of "precursor" or differences in the competence of cells to respond to an underlying prepattern. On the basis of this morphogenetic model, some of the experimental results, involving the genesis of novel patterns, and variation in the numbers and positions of structures are interpreted. The mechanisms responsible for the genesis of prepatterns are discussed. The prepattern is considered as the distribution of an inducing substance with regions of high and low concentration; the regions of high concentration occur at sites where structures later form. The process whereby such a distribution could arise is described. Various other mechanisms by which regular patterns involving larger number of structures can be formed are discussed.