Cells do not arise de novo but are formed from preexisting cells by reproduc­tion”, is one of the important attributes of the modern cell theory. Accordingly, every mul­ticellular organism, be it microscopic, or macro­scopic begins its existence as a single cell. This undergoes successive cycles of cell reproduction till an adult is formed. In a cell there exists a balance between the cytoplasm and the nucleus and the cell continues to grow till this balance is main­tained.

Continued growth of the cell culminates in partitioning of cytoplasm and nucleus into two daughter cells by cell division. Besides, cell divi­sion is essential for continuity of life.

Despite its complexity, cell division is a mistake-free and coordinated process. It in­volves three major steps like replication of DNA, division of nucleus and division of cyto­plasm. Of these, division of nucleus is known as karyokinesis and that, of cytoplasm, cytoki­nesis. Somatic cells divide by mitosis whereas germ cells are formed through meiosis.