The chiasmata formation is the indication of completion of crossing over and beginning of separation of chromosomes. The chiasmata formed when the chromosomal parts begin to repel each other except in the region where these are in contact. Thus, chiasmata formation is necessary for the separation of homologous chromosomes.

During zygotene or zygonema of meiotic prophase I, the chromosomes become shorter and thicker. The homologous chromosomes come to lie side-by-side in pairs.

Gene expression, protein synthesis, secretion, motility etc, do not happen during M-phase.

Karyokinesis is a series of uninterrupted changes before forming two daughter nuclei. Though karyokinesis is a continuous process, it has been divided into four phases. They are prophase metaphase, anaphase and telophase.

Bivalent of meiosis-I consists of four chromatids and two centromeres.

The various substages of prophase occur in meiosis are leptotene, zygotene, pachytene,diplotene and diakinesis.

The main reason for the difference between the two is that the separating sister chromatids during the meiosis-II differ genetically due to crossing over that had occurred during prophase-I. 

The cell cycle of yeast is about 90 minutes (1.5 hours) in duration and a human cell takes almost 24 hours to divide by mitosis.

There are two distinct type of cell divisions taking place in multicellular organisms One is mitosis in somatic cells for growth and healing of wounds and the other is meiosis in reproductive cells for producing gametes having half the number of chromosomes. It is essential to maintain the characters of the species.
More number of cells are produced in meiosis. Each division of mitosis results in the formation of two cells while in meiosis four cells are formed.

All these happen in the two haploid nuclei simultaneously.
(i) Prophase-II, takes short time. Spindle formation begins and the chromosomes become short. Two chromatids are joined to a single centromere. Nuclear membrane and nucleous disintegrate.
(ii) Metaphase-II At the equator, the chromosomes align at the equator and spindle is formed. The centromere of every chromosome is joined to the spindle fibre and centromere also divides.
(iii) Anaphase-II The daughter chromosomes are formed. Chromatids move towards their poles with the spindle fibres.
(iv) Telophase-II Reaching at the poles, chromosomes form nuclei which are haploid(n) daughter nuclei. Again nuclear membrane is constructed. Nucleous now becomes clearly visible.
Cytokinesis Occurs and four daughter cells are formed which are haploid (n). It may occur once or twice or only after the meiosis-II cell division.

Two phases of meiotic division: 
(i) Meiotic cell division is divided into two phases Meiosis I and Meiosis II. 
(ii) In the meiotic I division, the homologous chromosomes pair to form bivalents. Exchange of genetic material takes place. 
(iii) The chromosomes now separate and get distributed into daughter cells. 
(iv) Prophase I is divided into five sub-stages : Leptotene, Zygotene, Pachytene, Diplotene and Diakinesis. 
(v) During Metaphase I, the bivalents get arranged on equatorial plate with their arms on the plate but the centromere is directed towards opposite pole. It is followed by Anaphase I.



Fig. Stages of meiosis
(vi) Now the homologous chromosomes repel each other, and move to the opposite poles with both their chromatids. 
(vii) In this way each pole gets half the chromosomes number of the parent cell. 
(viii) In telophase I, the nuclear envelope and nucleolus again appear. Meiosis II is quite similar to mitosis. 
(ix) The centromere of each chromosome breaks, separating the chromatids, one each to a daughter cell.
(x) The meiotic cell division maintains the chromosome number of a species. 
(xi) As a result of meiotic division, the four daughter cells are formed with half the chromosome number (haploid) in each cell.

Cell division is significant in the following ways
(i) Cell multiplication Cell division is a means of cell multiplication or formation of new cells from pre-existing cells.
(ii) Continuity It maintains continuity of living matter generation after generation.
(iii) Multicellular organisms The body of a multicellular organism is formed of innumerable cells. They are formed by repeated divisions of a single cell or zygote. As the number of cells increases, many of them begin to differentiate, form tissues and organisms.
(iv) Cell size Cell division helps in maintenance of a particular cell size which is essential for efficiency and control of cell activities.
(v) Genetic similarity The common type of cell division or mitosis maintains genetic similarity of all the cells in an individual despite being different, i.e., structurally and functionally.

Difference between Mitosis and Meiosis

During microsporogenesis in flowering plants, the four daughter cells formed are equal in size. On the other hand, during megasporogenesis the four daughter cells formed are unequal in size. This can be seen in many other organisms also during the formation of male and female gametes. Meiosis usually leads to formation of equal sized male gametes and unequal sized daughter cells while forming female gametes.

cell division, cell reproduction or cell multiplication is the process of formation of new daughter cells from the pre-existing cell or parent cell.
It is three types
(i) Amitosis
(ii) Mitosis
(iii) Meiosis.
A cell divides when it attains the size and the nucleocytoplasmic ratio disturbs. The DNA duplication also causes a cell to divide.

The interphase, though called the resting phase, is the time during which the cell is preparing for division by undergoing cell growth and DNA replication.
The interphase is divided into three further phases
(i) G₁-phase (Gap-1)
(ii) S-phase (synthesis)
(iii) G₂-phase (Gap-2)
G₁-phase corresponds to the interval between mitosis and initiation of DNA replication. During G₁-phase the cell is metabolically active and continuously grows but does not replicate its DNA. S or synthesis phase marks the period during which, DNA synthesis or replication takes place and also the amount if DNA per cell gets doubled.
During the G₂ -phase, proteins are synthesised in preparation for mitosis, while cell growth continues.
Cell in this stage remains metabolically active, but no longer proliferate unless called on to do so depending on the requirement of the organism.

Three main events that occur in interphase are
G₁-phase (post-mitotic or pre-synthetic phase), S-phase (synthesising phase) and G₂-phase (post-synthetic or pre-mitotic phase).
Major events of each phase are
(i) G₁-phase is the longest phase during which synthesis of RNA and DNA takes place.
(ii) S-phase is the phase during which chromosomes replicated and prepare themselves for equal distribution.
(iii) G₂ -phase, is the phase in which synthesis DNA gets stopped. However, formation of RNA takes place.