differentiation

differentiation in biology, series of changes that occur in cells and tissues during development, resulting in their specialization. This, in turn, permits a greater variety of organisms. In plants, unspecialized cells, composing tissue called meristem , differentiate into vascular tissue (xylem and phloem; see wood ), supportive tissue (sclerenchyma), and storage tissue (parenchyma). In animals, the tissues of the gastrula stage of the embryo differentiate into specialized tissues. While it is not fully understood what initiates this processs, it is known that each of the specialized cells in an organism carries a full set of genes , with all of the organism's genetic information, but each specialized cell expresses only part of it. That is, each cell only transcribes that DNA that it needs to do its specific tasks (see nucleic acid ).

differentiation The occurrence of changes in the structure and function of groups of cells due to increased specialization in an organism.

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.