Genetic Mechanisms of Morphogenesis and Differentiation in Multicellular Organisms

The possibilities of evolution of such a system of genome reactions are very wide, because on the one hand stimuli (triggers, inducers) which are not the direct substrate of the reaction may be infinitely varied they may be biochemical, physico-chemical, physical, mechanical, and so on they may be global, specific, nonspecific, and so on. On the other hand, the parts of the genome undergoing activation or repression may also be very varied, and may exist in any spatial or temporal combinations. 

In this case an individual genome is modified under the influence of the environment not for the cell which it directly serves, but for other cells which, together with that one, form a cell system. 

Let us take the simplest example a group of cells (Fig. 103) leading a stable existence under conditions when environmental factors X, essential to life (such as products for chemical assimilation) act on one side, factors Z (e.g., oxygen) act on another, and factors Y (e.g., harmful products of neighboring groups of cells) 

The regulatory system S, A, and R may be activated (triggered) in response, not to the sum total of the factors composing X, Z, or Y, but to one t5 ical component, or to a typical companion of these factors. 

Differentiating factors of the external environment and inducing agents became to an increasing extent factors of an internal environment which constantly became more and more complex, as a result of interaction between genomes, and this laid the foundations of typical morphogenesis. 

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Molecular-Genetic Mechanisms of Morphogenesis and Differentiation in Multicellular Organisms... 

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