Dislocations in the Repetitive Unit Patterns of Biological Systems

Abstract

Periodicity, one of the most simple and frequent components of the process of pattern formation, observed in nonliving matter such as crystals or physical waves, is also present in living organisms. The architecture of an early animal or plant embryo depends upon the action of some master genes that section the 3-D space occupied by the growing population of embryonic cells into segments, organized along all three directions of growth (Alberts et al. [1], Howell [14]). The segments may be identical, as metamers emerging along the longitudinal axis of round or flat worms or muscles in a fish body, or plant modules such as nodes and internodes of the shoot. They may also assume a different identity due to the secondary processes of differentiation. Among numerous examples let us name just a few: the anterior and posterior segments of Drosophila larva, the concentric layers of dermal, ground and vascular tissues in plant cylindrical vegetative organs, the consecutive whorls of floral organs such as petals, stamens and carpels. These are the best known illustrations of the phenomenon in discussion. However there are many other examples of periodic patterns in biological systems. Some of them are rigid and represent a final product of certain developmental processes. Such for instance are the striped patterns of plant or animal body pigmentation (Fig. 1) or rippled patterns of its superficial sculpture (Fig. 2). Others, the most interesting, are dynamic, forming and frequently transforming in the course of an individual’s development. In our article we will present the latter as special cases being of special interest to our research group. They represent the greatest challenge in our attempts to produce their adequate description, which is possible only when the laws of their development are traced down.