Cell division ((कोशिका विभाजन))

Life cycle of a cell or cell cycle consist of metabolically active phase called inter phase and cell division phase which includes Karyokinesis and cytokinesis. Cell division is a process in which mother cell divides into two or more cells. Cell cycle involves 3 cycle a) Chromosomal cycle: in S-sub phase amount of DNA and Histone protein increase : it is reduce by karyokinesis b) Cytoplasmic cycle: In G1 and G2 sub Phase amount of Cytoplasm increases : it is reduce by cytokinesis c) Centrosomic cycle: centrosome arise and replicate in S-sub phase : it control both the above cycle and form mitotic poles.

Cell division is broadly categorized as-

Direct – karyokinesis (केन्द्रक का विभाजन) and cytokinesis (कोशिका द्रव्य का विभाजन) takes place simultaneously
Indirect – karyokinesis ((केन्द्रक का विभाजन)) is followed by cytokinesis (कोशिका द्रव्य का विभाजन)

कोशिकाओं का विभाजन तीन तरीकों से संभव है Cell division is of 3 types –

1. द्विखंडन (binary fission or amitosis)
2. समसूत्री विभाजन (mitosis)
3. अर्धसूत्री विभाजन (meiosis)

Amitosis – no spindal fiber formation

-Nuclear membrane does not disappear – Unequal distribution of genetic material -Occurrence of amitotic division : prokaryotes (bacteria, mvcoplasm, blue green algae) : eukaryotes (Tapetum cells, embryonic membrane of vertebrates, diseased tissue)

Mitosis – present in somatic cell therefore known as somatic cell division

– plants: stem tip and root tip – after this division the newly formed cell contain same amount of DNA as mother cell therefore called as equational cell division.