The 4 Differences Between Mitosis and Meiosis
Like any living structure, a cell body must have the capacity to leave offspring, that is, to transmit its genetic information throughout the generations. This is where the two terms that we’re analyzing today come into play: Mitosis and meiosis. We’ll show you the 4 differences between both fascinating processes.
All living beings are made up of cells, from one to millions of them. For example, according to scientific calculations, a young human weighing about 155 and 5 feet 7 inches meters tall contains some 30 trillion cell bodies in their body. 80-90% of them are found in the blood.
On the other hand, there’s also a wide range of beings with a single cell that makes up their entire body: Prokaryotes —bacteria and archaea—, certain fungi, protozoa, and diatom algae. The cell is the basic unit for life.
The cell: The basic unit of life
Before fully entering the world of cell division, it’s important to understand what a cell itself is. We’re talking about the basic unit of life, which is continuously multiplied to give rise to new individuals or to form and maintain tissues, organs, and systems.
As the Virtual Museum of Science indicates, Schleiden and Schwann’s cell theory emphasizes that all living beings are made up of cells and products made from them. This application is based on the following pillars:
- All living things are made up of cells.
- The cell is the anatomical and physiological unit of all living things.
- All cells are descendants of other ancestors.
- The hereditary material contained in the cell is passed from mother to daughter.
Each cell is an individualized entity separated from the environment by a membrane, with a cytosol in which various organelles, its own genetic material, and proteins and enzymes that support a complex metabolism thrive. No cellular component can exist outside of it.
The 4 differences between mitosis and meiosis
Once we’ve defined the limits of the cell, we’re ready to investigate the 4 differences between mitosis and meiosis. Both processes generate life because where before there was a cellular entity, after them, more have been generated. Even so, the two biological phenomena are different, with very different evolutionary meanings.
1. The definition is the key
According to the scientific portal Bioted.es, the growth and development of each living organism depend on the precise replication of the genetic material during each cell division. The DNA that’s passed between generations is made up of nucleotides, which code for specific genes organized on chromosomes.
Mitosis is defined as the process of nuclear division in which two nuclei are generated with the same number of chromosomes as the cell of origin. It precedes cell division, that is, the mechanism by which a parent cell divides into two daughter cells. This has two main functions:
- In unicellular organisms, it supposes a process of asexual reproduction. Where before there was only one bacterium, for example, now there are two that are equal to the parent.
- In multicellular organisms, cell division involves the development and formation of tissues that make up their complex physiological system. It’s also responsible for replacing damaged structures throughout the individual’s life.
Thus, mitosis has two key concepts enclosed in its definition: Asexual reproduction and the division of somatic cells, which make up the tissues of complex beings.
On the other hand, meiosis is defined as the process of nuclear division that gives rise to four cells with half the number of chromosomes of the cell of origin. This mechanism produces haploid sex cells (n) that, when united to form a zygote (2n), will give rise to a normal cell with half the genetic information from the mother and half from the father.
Therefore, we can affirm that:
Mitosis→ Parent cell (2n)→ daughter cell (2n) + daughter cell (2n)→ both are the same.
Meiosis→ Parent cell (2n)→ 4 haploid cells (n)→ sexual reproduction = zygote (2n).
We can put these concepts into perspective with human reproduction. A sperm and an egg are haploid (n) cells with 23 chromosomes. When the zygote is formed, these fuse giving rise to a diploid cell (2n) with 46 chromosomes, receiving one copy of each from the father and another from the mother.
2. Stages or phases of mitosis and meiosis
Mitosis and meiosis are also differentiated from each other based on the phases they present. We’ll explain this briefly below.
The phases of mitosis
- Prophase: The nuclear membrane disappears and the cell’s chromosomes undergo morphological changes. The centrosome divides into two centrioles and microtubules appear.
- Metaphase: Chromosomes line up in the center of the cell. It should be noted that each of them is made up of two sister chromatids.
- Anaphase: Microtubules pull each of the sister chromatids to one pole of the cell, each constituting a new chromosome. Therefore, in a human cell, 46 chromatids will go to one cell pole and another 46 to the other.
- Telophase and cytokinesis: Two new nuclear pockets are formed at each pole of the cell, the mitotic division material is broken down, and the cytoplasm is also split in two. Chromatids unwind inside each nucleus. Where before there was one cell (2n) there are now two (2n).
Mitosis is defined according to a previous interphase, and the chromosomes must self-replicate their genetic information so that each chromatid contains exactly the same information. According to the Complutense University of Madrid (UCM), mitosis is a universal process and is carried out practically in the same way in all living beings, although their functions are different.
The phases of meiosis
- Prophase I: The main difference between mitotic and meiotic prophase is that here, the pairs of chromosomes come together and form synapses. Each functional unit is a tetrad (2 chromosomes) or, at the same time, 4 chromatids.
- Metaphase I: In the case of the human being, the 23 tetrads (23×2 = 46 total chromosomes) or synapses are placed in the equator of the cell.
- Anaphase I: In this case, entire chromosomes instead of chromatids migrate to each cell pole. In other words, a chromatid doesn’t go away on each side, but two chromatids form the functional chromosome.
- Telophase I: The nuclear membrane forms in each pole nucleus, and the nucleolus begins to reorganize.
As you may have noticed, at this point the genetic information needs to be cut in half to give rise to haploid reproductive cells. For this reason, half of the cycle still remains, which now occurs in two daughter cells, instead of one parent:
- Prophase II: Very similar to mitotic prophase, except that the chromosomes aren’t drastically shortened.
- Metaphase II: Now, the monoploid number of chromosomes migrates to the equator of the cell. Each chromosome is made up of 2 chromatids, compared to the 4 chromatids of the tetrad in metaphase I.
- Anaphase II: Sister chromatids migrate to each pole of the cell. As in mitosis, each chromatid gives rise to its own chromosome.
- Telophase II: Cells divide into different cells. At the beginning of the prophase, there were 2 cells, and now there are 4 haploids.
The Complutense University of Madrid (UCM) also points out that in this process, an event called chromosomal crossover occurs. In tetrads formed in the early phases of meiosis I, genetic recombination occurs between homologous chromosomes, giving rise to recombinant chromosomes.
3. The evolutionary significance of mitosis and meiosis
This whole process is fascinating to the human eye, but what is the evolutionary significance of mitosis and meiosis? Of course, in each of the two cases, the answer is different.
According to the Department of Genetics at the University of Granada, all living mechanisms use mitosis, either as a reproductive tool or for individual growth. For a multicellular organism, the evolutionary significance of mitosis is to increase its number of cells, a fact that allows it to specialize in specific functions.
The evolutionary significance of meoisis is also clear: To generate genetic variability in offspring. If the sex cells were diploid (2n), the reproduction of each generation to follow would be increasingly convoluted, as the descendants would be 4n, 8n, 16n, and so on. This is incompatible with life.
In addition, the fusion of two different haploid cells and the genetic recombination of prophase I and metaphase I of meiosis are the basis, along with mutations, of the genetic variability of living beings. Each child is a new and completely different being, as they’re the result of the union of two different parents. This allows evolution to move forward.
4. A matter of numbers
To close this extensive journey through the world of mitosis and meiosis, we want to include in this last difference some numerical variables of each of the processes:
- In mitosis, 1 nuclear division occurs → In meiosis, 2 nuclear divisions occur.
- In mitosis, 2 daughter cells are produced with all the genetic material → In meiosis, 4 daughter cells are produced with half the genetic material.
- Mitosis has 4 phases → Meiosis has 8 phases.
In summary, an example of mitosis in humans would be the division of epidermal cells to renew the skin lost after an injury. Meiosis in humans would correspond to the formation of eggs and sperm. So complex, so simple.
Conclusions regarding mitosis and meiosis
As you may have read in these lines, both mitosis and meiosis are cell division processes, as from a single cell, 2 or 4 can be obtained with their own characteristics, depending on the mechanism described.
Even so, their functions are completely different. In multicellular beings, mitosis implies physiological complexity and tissue renewal, while meiosis is the way to give rise to descendants. In unicellular beings, mitosis is a form of asexual reproduction.It might interest you...
- Bianconi, E., Piovesan, A., Facchin, F., Beraudi, A., Casadei, R., Frabetti, F., … & Perez-Amodio, S. (2013). An estimation of the number of cells in the human body. Annals of human biology, 40(6), 463-471.
- La teoría celular, Museo Virtual de la Ciencia (CSIC). Recogido a 30 de noviembre en http://museovirtual.csic.es/salas/vida/vida6.htm
- Bioted.es. Protocolos, división celular. Recogido a 30 de noviembre en https://www.bioted.es/protocolos/DIVISION-CELULAR-MITOSIS-MEIOSIS.pdf
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