What is the difference between mitosis and meiosis?

Mitosis and meiosis are the two forms of cell division that occur in eukaryotic cells. Both share many similar stages and characteristics but also very important differences that have been key in the evolution of complex organisms.

Mitosis is a method of cloning, from a parent cell two descendant cells are obtained with the same genetic information and equal to the genetic information of the parent cell. In meiosis, however, four genetically different daughter cells are obtained from each other, and different from the parent cell, which are the basis of sexual reproduction.

General description

The mitosis part of a stem cell that divides into two daughter cells genetically the same and identical to the parent cell. The genetic material is duplicated, the nucleus splits in two (karyokinesis) and each nucleus is left with one copy of the genes. The cell then divides into two daughter cells (cytokinesis) and each keeps one of the nuclei. Each daughter cell receives an equal and complete copy of the genetic material of the parent cell.

mitosis occurs in somatic cells. These are the majority of cells that make up a multicellular organism and they do grow and develop. Each somatic cell has two sets of homologous genes, that is, they are cells diploid. In mitosis, these cells multiply, generating daughter cells that maintain the same genetic information. Daughter cells in mitosis remain diploid.

The meiosison the other hand, is the cell division that gives rise to four daughter cells each with a single set of genes. Daughter cells in meiosis are haploid. The genetic material of the parent cell is duplicated one timeas in mitosis, but the nucleus divides into four, each receiving a single set of genes.

meiosis occurs in the germ cellswhich are the precursor cells of gametes or sex cells. In the human they are gametes ovules and the sperm.

Thus, mitosis and meiosis start from a diploid cell that duplicates its genetic material to form four sets of genes. In mitosis half passes to each of the two daughter cells, so they remain diploid, but in meiosis four haploid daughter cells are formed with half the genetic information of the parent cell.

Different objectives: reproduction and growth

The goals of each type of cell division are the main difference between mitosis and meiosis from a biological point of view, especially as regards the reproduction and growth of organisms.

The function of mitosis is non-reproductive cell multiplicationthat is does not give rise to a new individual. Cell multiplication by mitosis generates a clone of the parent cell and is the basis for general growth of the organism and tissue repair.

Some authors consider that the multiple fission of some unicellular eukaryotic organisms is actually a mitosis. Here mitosis would have reproductive purposes as a method of asexual reproduction.

On the contrary, meiosis is for reproductive purposes only and occurs only in sexual reproduction. Sexual reproduction consists of the formation of a new diploid individual through the union of two gametes of different sexes, female and male, and the recombination of their genetic material. The genetic material of the new individual comes 50% from each of the parents.

Comparison of the phases of mitosis and meiosis

Interphase is the phase of the cell cycle that occupies most of the life of any cell. During this stage the cell performs its functions and metabolic tasks and in the end it divides or dies depending on numerous factors.

If it is going to divide, the cell replicates its DNA and centrioles, proteins in the cell nucleus that form the centrosomes. This phase of DNA replication is known as S interface. From here, depending on whether it is a somatic cell or a germ cell, it will enter mitosis or meiosis.

Both mitosis and meiosis share the same general phases:

  1. Prophase (in plant cells there is an additional earlier phase, the preprophase)
  2. Prometaphase
  3. metaphase
  4. Anaphase
  5. telophase
  6. cytokinesis or cell division

In mitosis there is a replication of DNA and a cycle of division phases. In meiosis there is a replication of DNA and two division cycles, meiosis I and mesiosis II, each with its prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis. When a single DNA replication occurs but two division cycles, four daughter cells are originated with half of the genetic information.

stages of mitosis

  1. ProphaseDNA during interphase is in the form of chromatin. On entering prophase the DNA, which was duplicated at S-interphase, condenses to form the comosomes (two chromatids joined by the structure called centromere). Both centrosomes, also formed at S interface, migrate to opposite ends of the cell. At the end of prophase, the nuclear membrane loses its organization and lets in microtubules to enter prometaphase.
  2. Prometaphase: the nuclear space is filled with microtubules that interact with the centromeres of the chromosomes.
  3. metaphase: centromere motor proteins (kinetochores) move the chromosomes through the microtubules until the chromosomes are aligned perpendicular to the centrosomes and the cell is formed. metaphase plate.
  4. Anaphase: the fibers of the metaphase plate pull each of the chromatids that form the chromosomes in the opposite direction until they separate them from the centromeres. Each chromatid migrates to opposite centrosomes..
  5. telophaseIt is the final phase of mitotic nuclear division. The metaphase plate dissolves and a nuclear membrane develops around the already separated chromatids. Already in the two new nuclei, the chromatids return to the form of chromatin.
  6. cytokinesis: it is a professed independent mitosis itself and is the phase that marks the end of the life cycle of the parent cell. Begins next to telophase and consists of the formation of a contractile ring of actin that strangulates the cell cytoplasm in the place where the metaphase plate was. The two nuclei are isolated in two daughter cells that begin Interphase again.

stages of meiosis

meiosis takes place in two division cycles, meiosis I and meiosis II. Each cycle goes through the same phases as in mitosis. In meiosis I a germ cell divides into two diploid daughter cells. In meiosis II, the daughter cells divide again into two but without prior DNA replication, which results in four haploid daughter cells.

The phases of meiosis I and meiosis II are slightly different from each other and from mitosis. One of the most important differences in the Chromosomal crossing over that occurs in prophase 1. In this phase, the chromatin condenses to form chromosomes and the nuclear membrane is disorganized, as in mitosis, but homologous chromosomes pair up, forming what are called tetrads and exchange DNA.

In anaphase 1 the tetrads separate on their respective chromosomes and move to opposite centrosomes. Telophase 1 develops, separating the nuclei and a first cytokinesis forming two diploid daughter cells. Due to chromosomal crossover, and unlike the daughter cells of mitosis, the two diploid daughter cells of meiosis 1 are not genetically identical to each other or to the parent cell.

Each of the daughter cells enters a new cycle of division, meiosis II, but without DNA replication. In anaphase 2, the centromeres of the chromosomes break, releasing each of the two chromatids that make up the chromosome. Each chromatid moves toward opposite centrosomes carrying a single set of genes.

In telophase 2, when the nuclear membranes form around the separated chromatids, another cytokinesis simultaneously begins, which will give rise to two more haploid daughter cells since they have a single set of genes. As we started from two daughter cells of meiosis 1, the end result is four haploid daughter cells formed from a single germ cell.

These haploid cells are gametes or reproductive cells. The union of two gametes and the recombination of your DNA to form a new diploid cell zygotefrom which a new individual will develop, is what defines the sexual reproduction.

Genetic variability and meiosis

The chromosomal crossing over that occurs in meiosis and the recombination of genetic information from two progenitor cells through the gametes, characteristic of sexual reproduction, introduces two of the most important factors of genetic variability that they know each other

Each daughter cell generated by mitosis is identical to the parent cell but the gametes produced by meiosis are different from each other and different from the parent cell. And also to obtain a complete individual, the union of two gametes is necessary. This allows to form individuals who inherit crossover genes from two parents and from their four "grandparents" greatly increasing genetic variability within the same species, a fundamental pillar of evolution.

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