differentiation

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differentiation The changes from simple to more complex forms undergone by developing tissues and organs so that they become specialized for particular functions. Differentiation occurs during embryonic development, regeneration, and (in plants) meristematic activity (see meristem). The mechanisms involved in the differentiation of cells and organization of tissues in animals has been most intensively studied in experimental organisms, notably the fruit fly Drosophila. In this insect the general body plan is established in the early embryo by proteins called morphogens, which are encoded by maternal genes of follicle cells and diffuse into the developing embryo. The various morphogens set up a pattern of concentrations that activates genes in different zones of the embryo to different extents, creating the basic pattern of body segments. A class of genes within the embryo itself, the segment genes, further refine this pattern. Within each segment the differentiation of appendages, such as limbs, is controlled by homeotic genes.

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