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developmental biology
Developmental biology is the study of the process by which animals and plants grow and develop, and is synonymous with ontogeny. In animals most development occurs in embryonic life, but it is also found in regeneration, asexual reproduction and metamorphosis, and in the growth and differentiation of stem cells in the adult organism. In plants, development occurs in embryos, during vegetative reproduction, and in the normal outgrowth of roots, shoots and flowers.
Practical outcomes from the study of animal developmental biology have included in vitro fertilization, now widely used in fertility treatment, the understanding of risks from substances that can damage the fetus (teratogens), and the creation of various animal models for human disease which are useful in research. Developmental Biology has also help to generate modern stem cell biology which promises a number of important practical benefits for human health.
== Perspectives ==
The main processes involved in the embryonic development of animals are: regional specification, morphogenesis, cell differentiation, growth, and the overall control of timing. Regional specification refers to the processes that create spatial pattern in a ball or sheet of initially similar cells. This generally involves the action of cytoplasmic determinants, located within parts of the fertilized egg, and of inductive signals emitted from signaling centers in the embryo. The early stages of regional specification do not generate functional differentiated cells, but cell populations committed to develop to a specific region or part of the organism. These are defined by the expression of specific combinations of transcription factors. Morphogenesis relates to the formation of three-dimensional shape. It mainly involves the orchestrated movements of cell sheets and of individual cells. Morphogenesis is important for creating the three germ layers of the early embryo (ectoderm, mesoderm and endoderm) and for building up complex structures during organ development. Cell differentiation relates specifically to the formation of functional cell types such as nerve, muscle, secretory epithelia etc. Differentiated cells contain large amounts of specific proteins associated with the cell function. Growth involves both an overall increase in size, and also the differential growth of parts (allometry) which contributes to morphogenesis. Growth mostly occurs through cell division but also through changes of cell size and the deposition of extracellular materials. The control of timing of events and the integration of the various processes with one another is the least well understood area of the subject. It remains unclear whether animal embryos contain a master clock mechanism or not.
The development of plants involves similar processes to that of animals. However plant cells are mostly immotile so morphogenesis is achieved by differential growth, without cell movements. Also, the inductive signals and the genes involved in plant development are different from those that control animal development.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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