Due to the irreversible character of the stepwise promotion the cells maintain their once obtained state of determination even if they escape from the influence of a morphogen source. This stability is possible without that the determination is absolutely fixed. In the regeneration of a cockroach leg, this process plays a decisive role. This avoids the necessity of a narrow time window to which the measurement is confined. Meanwhile several systems with this behaviour have been described.
Retinoic acid mimics the natural morphogen.
A transplantation to a posterior position, i.e., towards the presumptive morphogen source, leads to an adaptation to the new position, while a the pattern of gene activation is maintained after a transplantation to a more anterior position, i.e. away from the source. A widespread pattern in biology is segmentation, the reiteration of similar structures. The body segments of insects or the segments of insect legs are examples. Segments have an internal pattern, frequently visible by overt structures such as bristles or spines. The pattern within a segment has characteristic landmarks.