MITOSIS: The division of a cell to form two daughter cells each having a nucleus containing the same number and kind of chromosomes as the mother cell. The changes during divisions are clearly visible with a light microscope. Each chromosome divides lengthwise into two chromatids, which separate and form the chromosome of the resulting daughter nuclei. The process is divided into four stages, *prophase, *metaphase, * anaphase, and *telophase, which merge into each other. Mitotic division ensures that all the cells of an indivisual are genetically identical to each other and to the original fertilized egg.