Since all body cells are formed by mitosis and contain the same DNA information, it might be expected that they look and act alike; obviously, they do not. A human begins life as a single cell—a fertilized egg cell.
This cell reproduces to form 2 daughter cells; they in turn divide into 4 cells, the 4 become 8, and so forth. Then, sometime during development, the cells begin to specialize.
That is, they develop special structures or begin to function in different ways. Some become skin cells, others become bone cells, and others become nerve cells.
The process by which cells develop different characteristics in structure and function is called differentiation.
The mechanism responsible for this phenomenon is not well understood, but it may involve the repression of some of the DNA information.
Thus, the DNA information needed for general cell activities may be "switched on" in both nerve and bone cells. The information related to specific bone cell functions, however, may be repressed or "switched off" in the nerve cells.
Similarly, the information related to specific nerve cell functions would be repressed in bone cells. Although the mechanism of differentiation is obscure, the results are obvious. Cells of many kinds are produced, and each kind carries on specialized functions: skin cells protect underlying tissues, red blood cells carry oxygen, nerve cells transmit impulses. Each type of cell somehow helps the others, and aids in the survival of the organism.
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| Cell Differentiation |
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