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Meiosis n., plural: meioses Definition: a committed form the cell division that at some point gives increase to non-identical sex cells picture source: modification by Maria Victoria Gonzaga, lifwynnfoundation.org, from the functions of Marek Kultys (schematic chart of meiosis), CC BY-SA 3.0.


What is Meiosis?

A simple definition of meiosis would be is this: meiosis is the procedure of cell department that outcomes in the manufacturing of a haploid “daughter” cell through a haploid chromosomal variety of a diploid “parent” (“original”) cell. The resulting haploid cell after meiosis would have actually only one component of the various homologous chromosome pairs of the parent cell.

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Biology definition: Meiosis is a form of cell division in sexually reproducing biology wherein two consecutive nuclear divisions (meiosis I and meiosis II) take place without the chromosomal replication in between, causing the manufacturing of 4 haploid gametes, each containing among every pair the homologous chromosomes (that is, through the maternal and paternal chromosomes being spread randomly in between the cells).

Etymology: from Greek meiōsis, meioun (to diminish), from meiōn (less).


The main function of the meiotic department is the manufacturing of gametes (egg cells or sperm cells) or spores. In the person body, the meiosis process takes ar to decrease the variety of chromosomes in a regular cell i m sorry is 46 chromosomes to 23 chromosomes in eggs and sperms. So the variety of chromosomes in meiosis decreases to half. Consequently, throughout fertilization once the 2 haploid cell fuse, the number of chromosomes in the developed cell is revitalized as somatic cells (each v 46 chromosomes).

The procedure of meiosis is split into 2 parts, meiosis 1 and 2. Each component consists of 4 phases (prophase, metaphase, anaphase, and telophase), i m sorry is similar to mitosis by being comprised of four phases.

The very first part that meiosis (i.e. meiosis I) is the most facility part of the meiotic division. Prophase I, in particular, occupies almost an ext than fifty percent the time taken for meiosis as it has 5 substages: leptotene, zygotene, pachytene, diplotene, and diakinesis. The behavior and also organization of the chromosomes differ in each stage, which offers clues around the intricacy of prophase I.

Meiosis I can be differentiated from mitosis through three main features:

Meiosis I has actually reciprocal recombination (may also be dubbed chiasma formation and crossing over) Meiosis I has actually the pairing the the homologous chromosome The relax of the cohesion sister chromatids top top a two-step procedure occurs in Meiosis I.

These features enable the homologous distinction on the mitotic spindle. Then, the two sister chromatids separate during meiosis II. This various habits of the chromosome space described below for the distinctive events happening in each meiosis stage. Moreover, it need to be detailed that these occasions are interdependent. This method that the various events during the pairing the chromosomes, such together the recombination that reciprocal, the crossing-over, and the formation of chiasma room connected; therefore, the just successful procedure of recombination at meiosis ns prophase will certainly be the one that produces the correct homologous chromosome segregation at meiosis I.

The two succeeding chromosomal divisions result in the halving the the original variety of chromosomes. After ~ the perfect of S phase and also the production of similar chromatids native the replication that the parent chromosome, meiosis ns commence. The chromosomes start to pair with each other and also eventually segregate into two cells. The chromatids, though, remain together so each of the newly formed daughter cells will certainly contain one of the homologous chromosomes v two chromatids by the end of meiosis I.

Meiosis II follows Meiosis I. The two chromatids will then separate and segregate to 2 daughter cells. Therefore, in ~ the end of meiosis II, four daughter haploid cells are produced, each containing one copy of every chromosome.

After the replication of DNA, the pairing that the homologous chromosomes does no only permit for the distinction of meiotic chromosomes but also contributes come the recombination the maternal and paternal chromosomes. This pairing the chromosomes occurs throughout the prophase of meiosis I.


In meiosis, there space two succeeding nuclear divisions: very first meiotic department (or meiosis I) and 2nd meiotic division (or meiosis II). Every of them has four significant phases: prophase, metaphase, anaphase, and also telophase”’, and also are likewise designated as I or II, depending upon whether it wake up in meiosis ns or meiosis II.

Function that Meiosis

Why is meiosis essential for organisms? Imagine this, if gametes (eggs and sperms) to be to be developed by mitotic department only and also not be meiosis, then the gametes would certainly contain the same number of chromosomes as that that the diploid somatic cells. Consequently, as soon as the gametes fuse throughout fertilization, the resulting zygote will certainly contain 4 sets of the homologous chromosome and become tetraploid.

This scenario of “doubled chromosome content” will certainly go on come the next generations and also this leader to chromosomal aberrations. The chromosomal number is disrupted and also unkept throughout generations. This is, in fact, a case of chromosomal abnormality. Therefore, to store the variety of chromosomes consistent in each generation, gametes are produced by the procedure of meiosis, throughout the development of gametes, meiotic cell division decreases the number of chromosomes to haploid.

So what go meiosis produce? Meiosis starts v one round of replication the chromosomal DNA, then two steps of nuclear division. Together a result, four daughter nuclei (each of them is existing in a brand-new daughter cell) are created from the meiotic division of the original cell. Each daughter cell nucleus consists of only a haploid number of chromosomes. The formation of gametes haploid cells occurs in two rounds: Meiosis I and also II, through DNA replication for one time only (at S phase of interphase).

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Meiosis vs. Mitosis

What is the difference between meiosis and mitosis? Meiosis and mitosis room the two main forms of cell division. The differences in between them are summarized in Table 1.

Table 1: main differences in between meiosis and mitosis Meiosis Mitosis
Produces haploid cell (n) Produces diploid cells (2n)
Includes two nuclear divisions Includes one nuclear division
The product is gamete cell The product is somatic cell
Responsible for sexual reproduction Responsible for asexual reproduction
Crossing end takes place No cross over
Four cells room produced Two cells space produced

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Figure 1: comparison between meiosis and also mitosis stages.Credit: neighborhood College Consortium for Bioscience Credentials – Source, CC through 3.0.

Phases ofMeiosis

What is the process of meiosis? Meiosis is the process of four haploid cells development from a parent diploid cell. The measures of meiosis include 2 stages: meiosis I and meiosis II. Meiosis 1 definition: the an initial stage in the meiotic department or the reduction division of the meiosis. This is due to the fact that the number of chromosomes is diminished to fifty percent in this stage leading to the development of the haploid number of chromosomes.

Each pair of chromosomes come close together to exchange a part of their genetic material in a procedure or event called a synapse. This process occurs in the early on meiosis 1 stages, particularly during prophase I.

During prophase 1 of meiosis I, the homologous pair that chromosomes come really close together and also bind tightly to each various other so that they almost act as one single unit. This unit is called a bivalent or a tetrad (indicating the each chromosome is composed of 2 sister chromatids therefore the amount of bivalent is four chromatids). The bivalent splits right into two components after that is alignment in ~ the spindle equator so the each chromosome deserve to move to the spindle pole in ~ the the contrary side. Consequently, each newly formed daughter nucleus after ~ meiosis i is haploid since it has only one chromosome that the bivalent.

When perform sister chromatids separate? Meiosis II i beg your pardon is the second stage the the meiosis cell cycle is somehow similar to mitosis where the 2 daughter cells are formed as a result of the separation that each 2 chromatids. Therefore, meiosis i is the stage at i beg your pardon events distinct to the meiosis bike occurs. Nevertheless, each stage of the meiotic department is subdivided in a manner the resembles the mitotic division, such as prophase, metaphase, anaphase, and telophase. However, the prophase of the very first meiotic division is much more complex and much longer than the prophase of mitosis. In contrast, the prophase that the second meiotic division is simpler and shorter.

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Figure 2: meiosis diagram mirroring the chromosomal alters during different steps that meiosis.Credit: National person Genome study Institute
Meiosis in brief: prior to the cell enters meiosis, the chromosomes in a cell are replicated (during the interphase). In meiosis I, the chromosomes condense follow me the facility of the nucleusand pair through their homologues during crossing over. Next, the pairs of chromosomes separate and move to opposite ends of the cell. The cabinet divides because that the an initial time creating two cells. The two cells will undergo meiosis II wherein both of lock divide further into 2 cells, every containing one of every decoupled chromosome’s sister strands (chromatids), thus, producing four gene different, haploid cells.

A. Phases that meiosis I

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Figure 3: homologous chromosomes.

In the cell cycle, meiosis i takes ar after interphase where the chromosomes replicate at S phase. Next, the chromosomes condense during the early on stages the prophase I. Two centrosomes take trip to the two opposite poles of the cell preparing it for nuclear division. Homologous chromosomes consists of pairs of chromatids. These chromosomes type bivalents ~ pairing in bespeak to it is in aligned at the spindle equator throughout metaphase I. Even though homologous chromosomes space separated from each other throughout anaphase, the 2 sister chromatids continue to be attached together.

action 1: Prophase ns
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Figure 4: Synapse. Credit: Miguel Gutierrez – Source, CC BY-SA 4.0.

Prophase i is the most facility phase that meiosis I, that is further subdivided into 5 stages i beg your pardon are: leptotene, zygotene, pachytene, diplotene, and diakinesis.

The Leptotene stage starts through the chromatin fibers condensing into thread-like-fibers the resemble the created structure in ~ the beginning of mitosis. The zygotene stage includes further condensation of the yarn that permits them come be identified as individual chromosomes. Together a an outcome of synapsis, the bivalents ) type when the bag of chromosomes end up being tightly combine together. (See number 4)

The development of bivalent is critically necessary in the procedure of the exchange the the DNA segment containing the genetic material in between the two close chromosomes in a procedure known as crossing over. This process takes place during the pachytene stage. The matching segments that chromosomes exchange genetic information for the recombination the genes.

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Compacting of chromosomes to nearly less 보다 a quarter its length occurs during the pachytene phase as well. Throughout the diplotene stage, near the centrosome, the two chromosomes of each bivalent different from each other. However, the two chromosomes stay attached through chiasmata, which are connections existing at the website where the 2 homologous chromosomes exchange DNA segments.

During diplotene, the warrior resumes, chromosomes decondense, and also the cabinet stops the meiosis for a certain duration of time. At the beginning of the last stage that prophase I, the diakinesis, once the chromosomes are re-condensed to their maximum state that compaction, the centrosomes move further.

The chromosomes are just attached by the chiasmata. Here, the spindles form, the nucleoli disappear, and also the atom envelope disappears. The development of meiotic spindle starts and also the disintegration of the nucleoli room indications that meiosis prophase 1 ends and meiosis metaphase 1 begins.

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Figure 5: step of Meiosis Prophase ns in mouse as seen by immunoflourescence. SYCP1 & 3 mark the synaptonemal complex (on the chromosomes), CREST point out centromeres. L: Leptotene; Z: late Zygotene P: Pachytene; D: Diplotene. Credit: Qiao et al. Source, CC through 4.0.


action 2: Metaphase ns

During this phase, the bivalents move to the equator of the spindle after attachment to the microtubules making use of their kinetochores. This process of the bivalent activity to the cell equator is commonly confined to meiosis ns only and does not happen in the mitotic division. Over there are four chromatids in every bivalent, consequently, each bivalent includes four kinetochores as well. These kinetochores appear close to each other appearing as a single unit encountering the exact same pole that the cell. Such an arrangement enables the attachment of each kinetochore come the microtubules that the spindle pole on opposing side. This setup is the an initial step the sets for the separation of the chromosomes during the adhering to anaphase. At this stage, the bivalents room randomly arranged, accordingly, the paternal and maternal chromosomes space aligned come one pole the the cell, and also therefore, each newly created daughter cell will obtain a mixture the paternal and maternal chromosomes during their activity to opposing poles throughout anaphase.


Step3: Anaphase ns

The an initial step in anaphase contains the migration of homologous chromosomes come the spindle poles by the assist of their kinetochore. This step represents one of the key differences between meiosis and mitosis. In mitosis, the sister chromatids separate during mitosis as they room pulled come the the opposite poles. In meiosis, the two sister chromatids continue to be attached together and the homologous chromosomes move toward the spindle poles ~ separation. This results in the presence of a haploid number of chromosomes in each spindle pole at the finish of meiotic anaphase I. The process of chromatid separation during mitosis is mediated by cleaving the 2 sister chromatids v the help of an activated enzyme referred to as separase. To avoid the action of separase in meiosis, the cell produces a specific protein referred to as shugoshin that stays clear of the separation that chromatids through protecting the centrosomal site of the chromosome at which the cleavage process takes place.


action 4: Telophase i

The final phase the meiosis i is telophase 1, i beg your pardon is identified by the hike of chromosomes to the spindle poles. A nuclear envelope could be formed around chromosomes before cytokinesis to produce two daughter cells of haploid to adjust of chromosomes. Most of the time, the chromosomes condensation after the initiation that meiosis II.


results of meiosis i

By the finish of meiosis I, cytokinesis help in the manufacturing of two cells, each with a haploid nucleus. The chromosomes of each haploid cell will certainly each consists of 2 chromatids attached at the centromere.


B. Phases that meiosis II

Interphase meiosis begins after the finish of meiosis I and also before the beginning of meiosis II, this phase is not linked with the replication the DNA since each chromosome already consists of two chromatids that were replicated already before the initiation that meiosis i by DNA synthesis process. In brief, DNA is replicated before meiosis ns start at one time only. The phase of meiosis II or 2nd mitotic department has a purpose comparable to that of mitosis where the two new chromatids space oriented in two new daughter cells. Therefore, the second meiotic division is periodically referred to as separation department of meiotic division.


step 1: Prophase II

Prophase 2 is the phase that complies with meiosis i or interkinesis, the is identified by the nuclear envelope and also nucleolus disintegration and the chromatids thickening and shortening in prophase II, and also centrosomes replicate and also migrate come the polar side. Prophase II is simpler and much shorter than prophase I; it somehow resembles the mitotic prophase. ~ above the other hand, prophase II is different from prophase I since crossing end of chromosomes occurs throughout prophase i only and also not prophase II. Metaphase II starts at the finish of prophase II.


step 2:Metaphase II

Metaphase 2 that meiotic division is also similar to metaphase the mitotic division, however, only fifty percent the variety of chromosomes are present in metaphase II, metaphase II is identified by the chromosomal alignment in the center of the cell.


action 3: Anaphase II

It is the stage that comes after metaphase II, in this phase, the sister chromatids separate and move towards the poles of the cell. Anaphase II is comparable to mitotic anaphase, wherein both involve the separation the the chromatids. The kinetochore shortening leads to the movement of sister chromatids to the 2 ends of the cell.


action 4: Telophase II

Telophase is the final step of meiosis, throughout telophase II, four haploid cell are created from the two cells produced during meiosis I, nuclear membranes the the newly created cells are completely developed, and the cell are completely separated in ~ the end of this phase. However, during spermatogenesis in humans and other animals, the sperms are not totally functioning at the finish of the telophase II because they need to build flagella in order to duty properly.


results of meiosis II

Four haploid cells are created after telophase II and also cytokinesis, each daughter cell consists of only one chromosome the the two homologous pairs. The produced haploid cells contain a mixture of hereditary information indigenous the maternal and paternal chromosomes. This cells add to the genetic diversity amongst individuals the the same types as well as the evolutionary procedure of organisms.

figure 6: meiosis 1 vs meiosis 2, the main ethics of meiosis requires the replication that DNA followed by 2 stages of division, Meiosis I and II. Credit: Becker, Kleinsmith, and Hardin, “The world of the cell”.


Examples of Meiosis

Where walk meiosis occur? Meiosis is not minimal to one species, it is consisted of in the life cycle of assorted organisms such as fungi, plants, algae, animals, and humans.

What is the function of meiosis? Meiosis may produce spores or gametes depending on the varieties where in humans and also other pets meiosis to produce gametes (sperm cells and also egg cells) if in plants and also algae meiosis is responsible because that the production of spores.


Meiosis in plants and also algae

Plants and algae room multicellular organisms that exhibit both haploid and diploid develops of cell in their life cycle. This phenomenon is referred to as alternation of generations wherein the haploid spores are created by meiosis. This is also why that is dubbed sporic meiosis in plants and also algae. The created spores germinate and also undergo mitotic division giving climb to a haploid tree or a haploid alga. The gametes are developed by mitotic department from the currently existing haploid cells; therefore, the haploid type is called gametophyte. The gametes fuse throughout fertilization to develop the diploid kind of cells. The spores are created from the diploid form by meiosis. Therefore, the diploid form is dubbed the sporophyte.

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Figure 7: Alternation the generation in vascular plants.Credit: CNX OpenStax, CC BY-SA 4.0.

Meiosis in fungi

Fungi additionally have asexual and also sexual phases in their life cycle. The mycelium, in particular, may go into either the sexual phase or the asexual phase. As soon as it beginning the sex-related phase, the haploid mycelia experience plasmogamy (the combination of the two protoplasts) and also karyogamy (the combination of 2 haploid nuclei). Thus, following karyogamy is the development of the diploid zygote.

The zygote grow to a stalked sporangium, which by then, will type haploid spores by meiosis. The spores produced by meiosis are called meiospores in contrast to mitospores that are produced via mitosis. These haploid spores (reproductive cells) will certainly be released from the sporangium and each will at some point germinate right into a brand-new mycelium. Thus, in fungi, meiosis is the 3rd step in the sequential step of the sexual phase where plasmogamy is the first followed by karyogamy. Meiosis is crucial in restoring the haploid state the the fungus. Check out the number below.

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Figure 8: Zygomycete life cycle. Credit: CNX OpenStax.

Meiosis in humans and other animals

How walk meiosis work in humans? Meiosis produces haploid gametes in humans and other animals. The is a an essential part of gametogenesis. Together the surname implies, gametogenesis is the biological procedure of creating gametes. In humans and also other animals, there room two forms of gametogenesis: spermatogenesis (formation of male gamete, i.e. Sperm cell) and oogenesis (formation the the female gamete, i.e. Ovum or egg cell).

In oogenesis, four haploid gamete cell are produced from a diploid oocyte. However, just one cabinet survives and also functions as an egg; the various other three become polar bodies. This result results from the unequal department of the oocyte by meiosis where among the created cells receives many of the cytoplasm of the parent cell if the other created cells degenerate i m sorry contributes to enhancing the concentration that the nutrient in the formed egg. The egg cell acquires many of its dedicated functions during phases that meiosis specifically prophase I.

In spermatogenesis, the sperm repurchase its specialized features in stimulate to develop into a practical gamete after ~ meiosis and post-meiotic events, e.g. Spermiogenesis wherein the sperm cell matures by obtaining a functional flagellum and also discarding most of their cytoplasm to type a compacted head.

When go meiosis occur? Meiosis occurs during the reproductive phase of the organism. In humans, though, the meiotic department occurs at various stages. For instance, in males, the starts in ~ puberty and also persists throughout your lifetime. In females, the child will already have major oocytes arrested in ~ prophase I and also will proceed the next stages that meiosis at puberty. However, as each main oocyte establishes into a secondary oocyte in ~ ovulation, it will prevent again at metaphase II that meiosis II. Meiosis will only proceed and also reach perfect at fertilization. If no fertilized, meiosis will no longer proceed and also the arrested secondary oocyte will disintegrate. Soon, menstruation begins.

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Figure 9: Spermatogenesis. Credit: Alberts et al. (2002). NIH books

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Figure 10: Oogenesis. The oogonium (A) experience mitosis and (B) distinguish into a primary oocyte. Meiosis I begins (C). (D) Meiosis ns is completed, producing secondary oocyte and also (E) and also the first polar body. The second oocyte is released from the follicle at ovulation (G). The existence of sperm penetration (fertilization) root cause the secondary oocyte to finish meiosis II to develop the ovum (H) and also the second polar body (I). Credit: Leiladavids – Source, CC BY-SA 4.0.

Errors in Meiosis

Meiosis is susceptible to errors., and therefore, can impact the capability of the human being to reproduce. Abnormal meiosis has actually a great negative influence on person perpetuity. Errors in meiosis procedures can an outcome in infertility as well as the development of gametes of genetically imbalanced features. Meiotic errors room the main contributors come the congenital abnormalities resulting from hereditary impairment and the mental abnormalities affecting newborn children.

Errors in the pairing and recombination that chromosomes are existing in much more than 30% of the human being oocyte pachytene whereby the pairing that homologous chromosomes fails, in a phenomenon known as asynapsis.

In yeast, fail in the chromosomal pairing have the right to lead to cell death after triggering the checkpoints of the cell. The exact same phenomenon is it was observed in the germ cell of humans. Consequently, the increase in the oocytes with errors in the chromosomal pairing will cause the depletion in the variety of germ cells that result in premature birth menopause in women. Similarly, errors in the stages of meiosis of spermatocyte production result in infertility due to the decrease in the number of functional sperms produced.

Depletion in the variety of germ cells is more far-reaching in females 보다 in males due to the fact that the male produces around 300-400 million sperms daily whereas ladies produce about 300-400 oocytes during her lifetime.

At metaphase I, chromosome pairs could fail come cross end properly, therefore, the unpaired chromosomes segregate randomly through an enhanced risk that the production of aneuploid gamete, which consists of an imbalanced number of chromosomes copies. Moreover, spermatocytes may be got rid of by apoptosis or necrosis as result of failed crossing-over.

Biological importance of Meiosis

What is the role of meiosis in reproduction? for every organ that reproduces sexually, meiosis and mitosis room two essential parts of their cell cycle due to the fact that of the balance between the number of chromosomes that room doubled throughout fertilization and also the halving of chromosomes during gamete development by meiosis is maintained. A sexually reproducing organism has actually a cabinet cycle that consists of two key phases: a haploid phase and also a diploid phase. Meiosis meaning biology is the haploid phase the starts during gamete formation and also ends with the formation of zygote during fertilization wherein the diploid phase starts at the formation of a zygote by the fusion of 2 gametes and also ends by meiotic cell division during gamete formation.

How countless cells are created in meiosis? The meiotic division produces four haploid cells from one diploid cabinet to finish the life bicycle of sexually reproduced organisms such together humans and animals. Prior to meiosis, in the parent diploid cell, the chromosomal DNA duplicates, moreover, 4 haploid nuclei are developed as a result of two successive departments of a diploid nucleus.

Why is meiosis important for organisms? Meiosis is biologically important due to the fact that it is responsible for the genetic diversity amongst sexually reproduced biology where during prophase I, the chromatids of the two homologous chromosomes synapse and exchange parts of their hereditary materials.

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Meiosis is a crucial process due to the fact that it to reduce the original number of chromosomes come half, and permits genetic variability by genetic recombination and also independent assortment. Meiosis produces four haploid cells that may construct into potential gametes so that once fertilization occurs, a new individual with the full variety of genes results, thereby preserving the verity of chromosomal number throughout generations while cultivating genetic diversity and variability in creates in the population.