Meiosis: definition and phases
Meiosis: definition and phases
What is meiosis
The term meiosis comes from the Greek μείωσις (meíōsis), which means "decrease". Meiosis is a process of cell division by which four haploid cells are produced from a diploid cell.
Haploid cells are cells that contain a set of chromosomes. Gametes or sex cells (eggs and sperm) are haploid cells.
The goal of meiosis is to generate sex cells. It is for this reason, when a sperm and an egg unite in fertilization, their two haploid sets of chromosomes unite to form a whole new diploid set, that is, DNA or genome. completely new.
Meiosis and fertilization are the basis of sexual reproduction and genetic variability within populations. They are also responsible for the ability of species to evolve.
Phases of meiosis
Meiosis occurs through a two-stage cell division process: meiosis I and meiosis II. Meiosis I is the phase of reductional division, in contrast, meiosis II is the phase of equational division. In meiosis I (reductional division), a diploid cell divides into two haploid cells.
However, in meiosis I (equational division), each haploid cell divides into two haploid cells. Thus, each diploid mother cell divides into 4 haploid daughter cells during meiosis.
Meiosis I
Meiosis I, also known as the reducing phase, is the phase in which pairs of homologous cells separate, causing the genetic material of daughter cells to be half that of progenitor cells. This is what generates genetic diversity.
Meiosis I is subdivided into four phases:
- Prophase I: the chromosomes condense and form pairs. Cross-linking and genetic recombination occur, allowing parts of DNA strands to be exchanged to give rise to new genetic material.
- Metaphase I: Homologous pairs line up on the metaphase plate for separation to occur.
- Anaphase I: Chromosomes separate by moving to opposite ends of cells, while sister chromatids stay together.
- Telophase I: haploid cells are formed. Each chromosome will have two sister chromatids, which will not be the same as each other.
Meiosis II
Meiosis II, also known as the duplication phase, is the stage in which the chromatids separate, producing a pair of daughter cells each containing 23 chromosomes. Each chromosome will, in turn, produce a single chromatid.
- Prophase II: the chromosomes condense.
- Metaphase II - chromosomes line up on the metaphase plate.
- Anaphase II: Sister chromatids separate at opposite ends of the cell.
- Telophase II: Newly formed gametes are haploid. Each chromosome has a single chromatid. The end product of meiosis is the sperm or the eggs. Importance of meiosis
Meiosis is a process of vital importance for living beings, it allows to carry out the life cycle, because it allows the survival of the species by producing sex cells or gametes, as well as genetic recombination. As a result, meiosis promotes genetic variability between organisms of the same species which, although they share and inherit a series of characteristics, are unique beings because their genetic information is new.
It is also noteworthy that the genetic recombination of the chromosomes of the father and the mother occurs at random in the processes which correspond to Anaphase I and Anaphase II.
Scheme of meiosis
The two phases of meiosis can be schematized as follows:
Meiosis and Mitosis
Meiosis and mitosis are the different forms of cell division. In meiosis, sex cells or gametes are generated, i.e. ovaries and sperm; it is the basis of sexual reproduction and is essential for genetic variability.
The result of meiosis is the production of cells with different genetic material. Mitosis, on the other hand, is the process of cell division in which new cells are generated with identical genetic material. In this sense, mitosis is the cellular process responsible for asexual reproduction. It is essential for the growth and regeneration of tissues.