Mitosis and meiosis are the two types of mechanisms involved in cell division and reproduction of all multicellular organisms. Mitosis occurs in all living organisms on earth except viruses. Meiosis occurs only in animals, plants, and fungi. Both mitosis and meiosis start with diploid parent cells. By mitosis, two identical daughter cells are produced. By mitosis, four haploid gametes are produced. Mitosis occurs in somatic cells in the body of multicellular organisms and meiosis only occurs in germ cells.
Key Areas Covered
1. What is Mitosis
– Definition, Stages, Process, Function
2. What is Meiosis
– Definition, Stages, Process, Function
3. What are the Similarities Between Mitosis and Meiosis
– Outline of Common Features
Key Terms: Anaphase, Anaphase I, Anaphase II, Cell Division, Daughter Cells, Diploid, Haploid, Gametes, Metaphase, Metaphase I, MetaphaseII, Meiosis, Mitosis, Parent Cells, Prometaphase, Prophase, Prophase I, Prophase II, Somatic Cells, Telophase, Telophase I, Telophase II
What is Mitosis
Mitosis is a type of cell division, which produces two daughter cells identical to the parent cell. Mitosis is seen in ordinary tissue growth and repair, increasing the somatic cell number of the body. The mitosis is a process of nuclear division, which is always followed by the division of cytoplasm, cytokinesis. Typically, a diploid cell which completes its interphase undergoes mitosis. The interphase is composed of G1, S and G2 stages. The cell’s highest rate of metabolic activity can be observed during the interphase. DNA replication, protein synthesis, and the synthesis of organelles occur during interphase. The prophase, prometaphase, metaphase, telophase, and the anaphase are the stages of mitosis.
The chromatin in the nucleus is condensed and become visible as chromosomes during prophase. The nucleolus disappears. Since the two centrioles move to opposite poles, the mitotic spindle begins to form.
The nuclear membranes are dissolved and the kinetochore proteins are formed in the centromeres of chromosomes during the prometaphase. Microtubules of the mitotic spindle attach to the kinetochore proteins.
The individual chromosomes are aligned along the cell equator with the help of the mitotic spindles, ensuring the proper segregation of sister chromatids into the two daughter cells.
During anaphase, sister chromatids are separated from their centromeres. The separated sister chromatids begin to move towards the opposite poles of the cell.
During telophase, sister chromatids arrive at the two opposite poles and new nuclear membranes are formed around the two daughter nuclei.
After undergoing the nuclear division, the division of the cytoplasm or the cytokinesis begins with the arrangement of actin fibers around the center of the cell in animals. The contractions of actin fibers result in the pinching of the parent cell into two daughter cells. In plants, a rigid cell wall is formed at the middle of the parent cell, separating it into two. The stages of mitosis are shown in figure 1.
Read more: What are the Stages of Mitosis
What is Meiosis
Meiosis is the other type of cell division which only occurs during gametogenesis in germ cells of gonads. In meiosis, four daughter cells are produced by undergoing two, sequential nuclear divisions to produce gametes containing a half of the original number of chromosomes. The production of gametes with half of the chromosome number of a particular species is important to maintain exact chromosome number of the species during sexual reproduction. The fusion of the two gametes regenerates the ordinary chromosome number.
Cells undergo nine stages in the nuclear division during the process of meiosis, which can be divided into two major stages as meiosis I and meiosis II. Meiosis I is composed of an interphase, prophase I, metaphase I, anaphase I, telophase I and cytokinesis. Meiosis II is composed of prophase II, metaphase II, anaphase II, telophase II and cytokinesis. For the two nuclear divisions, only one interphase is found in which DNA replication, Protein synthesis, and organelle synthesis take place in the cell.
During prophase I, chromosomes become visible due to the condensation of chromatin. The pairing of homologous chromosomes occurs, allowing the homologous recombination of genetic material through crossing over of parts of the homologous chromosomes. The nuclear membranes also disappear.
During metaphase I, homologous chromosome pairs align along the cell equator. The meiotic spindle begins to form, extending microtubules towards the centromeres of chromosomes. Microtubules of the meiotic spindle are attached to the centromere of each homologous chromosome in the pair.
During anaphase I, each chromosome in the homologous pair is pulled apart by the meiotic spindle. The two sister chromatids of the chromosome stay together during meiosis I.
Telophase I and Cytokinesis
In telophase I, a full set of individual chromosomes can be found in each of the two opposite poles of the cell. The nuclear membranes are formed surrounding each of the two daughter nuclei. The cell pinches from the middle to separate into two daughter cells in cytokinesis.
Prophase II occurs in the daughter cells as a result of meiosis I. Each of the daughter cells comprises an individual chromosome set with two sister chromatids. The nuclear membranes disappear during prophase II and the formation of the second meiotic spindle begins.
Individual chromosomes are aligned at the cell equator during the metaphase II. The microtubules of the second meiotic spindle are attached to the centromere of the each individual chromosome in both sides.
Sister chromatids are pulled apart towards the opposite poles of the cell due to the contractions of the meiotic spindle. Each sister chromatid moves to opposite poles.
Telophase II and Cytokinesis
Each set of sister chromatids can be found at opposite poles of the cell in the telophase II. The second two daughter nuclei are formed and surrounded by nuclear membranes. The division of the cytoplasm produces two granddaughter cells from each of the daughter cell of meiosis I. The resulting granddaughter cells are differentiated into sperm cells in males and egg cells in females. The stages of meiosis are shown in figure 2.
Read more: Difference Between Meiosis 1 and Meiosis 2
Similarities Between Mitosis and Meiosis
- Mitosis and meiosis are two mechanisms involved in the reproduction of multicellular organisms.
- Both mitosis and meiosis start from a diploid parent cell.
- Both mitosis and meiosis are processes of nuclear division of cells.
- The major steps of both mitosis and meiosis are interphase, prophase, metaphase, telophase, and anaphase.
- The DNA of the parent cell is replicated prior to nuclear divisions.
- Mitosis is similar to meiosis II.
- During the metaphase of mitosis and the metaphase II of meiosis, individual chromosomes are arranged in the cell equator.
- During the anaphase of mitosis and the anaphase II of meiosis, sister chromatids are separated to opposite poles.
- Both mitosis and meiosis end in cytokinesis.
Read more: Difference Between Mitosis and Meiosis
Mitosis and meiosis are two types of cell divisions that occur in higher organisms such as animals, plants, and fungi. Mitosis occurs in the somatic cells and it is involved in growth and repair. Meiosis occurs in the germ cells in gonads and it produces daughter cells with a half number of chromosomes to the parent cell. Meiosis is involved in maintaining a constant chromosome number in somatic cells. Both mitosis and meiosis occur through most identical stages of nuclear divisions.
1. “Mitosis.” The Cell Cycle & Mitosis Tutorial. N.p., n.d. Web. Available here. 16 July 2017.
2. “What is meiosis?” Facts. The Public Engagement team at the Wellcome Genome Campus, 06 May 2016. Web. Available here. 16 July 2017.
1. “Mitosis diagram” By Marek Kultys – Own work(own work by uploader).Źródło (source): (CC BY-SA 3.0) via Commons Wikimedia
2. “Meiosis diagram” By Marek Kultys – Own work (CC BY-SA 3.0) via Commons Wikimedia