CELL DIVISION
8.1 Objectives
8.2 Introduction
8.3 Cell cycle, stages, mitosis, cytokinesis
8.3.1 Cell cycle
8.3.1.1 Phases of cell cycle
8.3.1.2 Control of cell cycle
8.3.2 Mitosis
8.3.2.1 Karyokinesis
8.3.2.2 Cytokinesis
8.3.2.3 Significance of mitosis
8.4 Meiosis
8.4.1 Divisions of meiosis
8.4.1.1 First meiotic division or Meiosis-I
8.4.1.2 First meiotic division or Meiosis-II
8.4.2 Cytokinesis
8.5 Comparison between mitosis and meiosis
8.6 Summary
8.7 Glossary
,8.8 Self Assessment Questions and Possible Answers
8.8.1 Multiple Choice Questions
8.8.2 Very Short Questions
8.9 References and suggested readings
8.10 Terminal and Model Questions
8.1 Objectives
After reading this unit the readers will be able to:
Define mitosis and meiosis.
Elucidate stages of cell cycle.
Explain cytokinesis.
Describe reproductive cycle stages and synaptonemal complex.
Discuss recombination nodules.
Compare between mitosis and meiosis.
8.2 Introduction:-
A multicellular organism starts its life as a single cell and it undergoes repeated
division, thus, the growth and development of every living organism depends on the
growth and multiplication of its cells. The cell increase in size due to growth and it is the
characteristic feature of all the living organisms. After the cell attains maximum growth,
it begins to divide. The vegetative growth of an organism takes place by an increase in
the number of cells through cell divisions which follows the geometrical progression. The
cell division is a continuous and dynamic process and it involves the following three
stages:
1. DNA or genome replication
, 2. Nuclear division or karyokinesis
3. Cytoplasmic division or cytokinesis
The cell division is of two types on the basis of number of genomes present in the
daughter cells in comparison to the dividing parent cell — mitosis and meiosis.
1. Mitosis- The term mitosis was coined by W. Flemming in 1882. The
multiplication of a body cell into two daughter cells of equal size and
containing the same number of chromosomes as in the parent cell is called
mitosis or somatic division.
2. Meiosis- The term meiosis was first coined by J. B. Farmer (1905)
with J. E. Moore. Meiosis occurs only in gonads (in germ mother cells) during
the formation of gametes like sperm and ovum. Meiosis is a process by means
of which double number or 2N or diploid chromosomes is reduced to its half
number or N or haploid. It is also called reduction process.
8.3 Cell Cycle Stages, Mitosis & Cytokinesis :-
8.3.1 Cell Cycle:-
Every cell having the capacity to divide passes through a regular cycle of changes
known as cell cycle. A cell starts its cycle in diploid condition.
8.3.1.1 Phases of cell cycle:-
Cell cycle consists of two stages: A long un-dividing stage called interphase or
Iphase and a short dividing stage called mitotic or M-phase (Fig. 8.1).
8.1 Objectives
8.2 Introduction
8.3 Cell cycle, stages, mitosis, cytokinesis
8.3.1 Cell cycle
8.3.1.1 Phases of cell cycle
8.3.1.2 Control of cell cycle
8.3.2 Mitosis
8.3.2.1 Karyokinesis
8.3.2.2 Cytokinesis
8.3.2.3 Significance of mitosis
8.4 Meiosis
8.4.1 Divisions of meiosis
8.4.1.1 First meiotic division or Meiosis-I
8.4.1.2 First meiotic division or Meiosis-II
8.4.2 Cytokinesis
8.5 Comparison between mitosis and meiosis
8.6 Summary
8.7 Glossary
,8.8 Self Assessment Questions and Possible Answers
8.8.1 Multiple Choice Questions
8.8.2 Very Short Questions
8.9 References and suggested readings
8.10 Terminal and Model Questions
8.1 Objectives
After reading this unit the readers will be able to:
Define mitosis and meiosis.
Elucidate stages of cell cycle.
Explain cytokinesis.
Describe reproductive cycle stages and synaptonemal complex.
Discuss recombination nodules.
Compare between mitosis and meiosis.
8.2 Introduction:-
A multicellular organism starts its life as a single cell and it undergoes repeated
division, thus, the growth and development of every living organism depends on the
growth and multiplication of its cells. The cell increase in size due to growth and it is the
characteristic feature of all the living organisms. After the cell attains maximum growth,
it begins to divide. The vegetative growth of an organism takes place by an increase in
the number of cells through cell divisions which follows the geometrical progression. The
cell division is a continuous and dynamic process and it involves the following three
stages:
1. DNA or genome replication
, 2. Nuclear division or karyokinesis
3. Cytoplasmic division or cytokinesis
The cell division is of two types on the basis of number of genomes present in the
daughter cells in comparison to the dividing parent cell — mitosis and meiosis.
1. Mitosis- The term mitosis was coined by W. Flemming in 1882. The
multiplication of a body cell into two daughter cells of equal size and
containing the same number of chromosomes as in the parent cell is called
mitosis or somatic division.
2. Meiosis- The term meiosis was first coined by J. B. Farmer (1905)
with J. E. Moore. Meiosis occurs only in gonads (in germ mother cells) during
the formation of gametes like sperm and ovum. Meiosis is a process by means
of which double number or 2N or diploid chromosomes is reduced to its half
number or N or haploid. It is also called reduction process.
8.3 Cell Cycle Stages, Mitosis & Cytokinesis :-
8.3.1 Cell Cycle:-
Every cell having the capacity to divide passes through a regular cycle of changes
known as cell cycle. A cell starts its cycle in diploid condition.
8.3.1.1 Phases of cell cycle:-
Cell cycle consists of two stages: A long un-dividing stage called interphase or
Iphase and a short dividing stage called mitotic or M-phase (Fig. 8.1).
