Peculiarity of Mitosis involved in Cleavage
Though, the mitosis involved in cleavage and the mitosis occurred in late embryos and in adult animals, is fundamentally same, but, both differ in following aspects:
1. In the later embryonic stages and in the adult, the mitosis is intimately connected with growth. After each mitotic cell division the daughter cells grow and when they are approximately doubled in size they divide again. The cells, thus, maintain an average size in every type of tissue. During cleavage this is not so. The consecutive divisions of the blastomeres are not separated by period of growth. A blastomere does not increase in size before the next division begins. Consequently, with each division the resulting blastomeres are only half the original size. Thus, cleavage begins with one very large cell and ends with a great number of cells, each of which is no longer very much larger than the tissue cells of the adult animal.
2. The intermitotic interval or interphase remains very short in mitosis involved in cleavage.
3. During cleavage, the division of nucleus (karyokinesis) of fertilized egg or blastomere, usually is followed by division of cytoplasm (cytokinesis) like the mitosis of somatic cells, but, in certain animals each karyokinesis is not immediately followed by cytokinesis.
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