This leads also to a limitation of the inhibitor production. More cells become activated at a lower level until sufficient inhibitor is produced. In other word, the activated regions have the tendency to enlarge, However, in order to become activated, a close neighbourhood to non-activated cells is essential into which the inhibitor can be dumped. Both requirements, large activated patches and a direct neighbourhood of non-activated cells, seems to contradict each other. This is, however, not the case.
Stripe formation is a very frequent phenomenon at very different developmental situations.
Usually the size of a morphogenetic field increases during the growth of the embryo. In a usual reaction-diffusion system a graded concentration profile can be maintained only over a range of about a factor two. This is inappropriate if the graded concentration should be used in the growing embryo as positional information for the determination of the primary body axes. Multiple maxima would lead, for instance, to several heads instead of one. Some basic biological observations provide important hints of how this wave length problem has been solved by nature.