In biological cells that divide, cell division can occur after DNA replication. Cell growth, which occurs throughout the cell cycle, typically causes a cell to double in size by the time it is ready to divide. Certain types of cells, however, undergo an asymmetric division process. In all organisms in which development has been studied extensively, ranging from bacteria to mammals, asymmetric cell division is one of the apparent origins of cell diversity.
Extrinsic mechanisms involve cell-cell communication.
Interactions between daughter cells or between a daughter cell and other nearby cells can specify daughter cell fate. Recent studies have indicated that a combination of intrinsic and extrinsic mechanisms specify distinct daughter cell fates during asymmetric cell division. The microtubules are 25 nanometers in diameter, and composed of the protein tubulin. They occur in regular arrays in cilia, flagella, the mitotic spindle, and in the cytoplasm in general, and they contribute not only to cell shape, but also to cell motility. Among important distinguishing characteristics of metazoa are cell differentiation and intercellular communication.