Meiosis involves two sequential cycles of nuclear and cell division, but only a single cycle of DNA replication. Meiosis is divided into meiosis I and meiosis II.
- Meiosis I begins after the S phase, and meiosis II follows meiosis I.
- Pairing of homologous chromosomes happens during meiosis which results in recombination of genes.
- Four haploid daughter cells are formed at the end of meiosis.
|Meiosis I||Meiosis II|
|Prophase I||Prophase II|
|Metaphase I||Metaphase II|
|Anaphase I||Anaphase II|
|Telophase I||Telophase II|
- Chiasmata is terminated at this stage.
- Meiotic spindles are formed to prepare the homologous chromosomes for separation.
- Nucleolus disappears and nuclear envelope breaks down by the end of diakinesis.
- The bivalent chromosomes are aligned on the equatorial plate.
- Spindle fibres from opposite poles attach to the pair of homologous chromosomes.
Homologous chromosomes separate, but sister chromatids remain attached at their centromeres.
- Nuclear membrane and nucleolus reappear.
- This is followed by cytokinesis and this stage is called the diad of cells.
The stage between the two meiosis divisions is called interkinesis. Interkinesis is usually short lived.
Prophase II: Meiosis II resembles the mitotic cell division. It begins immediately after cytokinesis. Nuclear membrane disappears. Chromosomes again become compact.
Metaphase II: The chromosomes align at the equator. Spindle fibres from the opposite poles get attached to the kinetochores of sister chromatids.
Anaphase II: Centromeres split and sister chromatids move towards the opposite poles.
Telophase II: The two groups of chromosomes get enclosed by nuclear envelope. This is followed by cytokinesis; resulting in the formation of four daughter cells.
Significance of Meiosis:
- Conservation of specific chromosome number of each species is achieved across successive generations in sexually reproducing organisms through meiosis.
- Meiosis helps in increasing the genetic variations in the population of organisms from one generation to the next.
|Difference Between Mitosis and Meiosis|
|This type of division takes place in somatic cells.||This type of division takes place in gametic cells.|
|Two daughter cells are formed.||Four daughter cells are formed.|
|Number of chromosomes remains diploid in daughter cells.||Number of chromosomes becomes haploid in daughter cells. |
|Mitosis is necessary for growth and repair.||Meiosis is necessary for sexual reproduction.|
|Crossing over does not take place.||Crossing over takes place.|