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The indigenous meiosis originates native the Greek language. It method to lessen; this refers to the lessening of the number of chromosomes in ~ the cell. Meiosis is the procedure of chromosomal palliation in eukaryotic bio cells (plants, animals, and also fungi), which leads to the manufacturing of germ cells (gametes/sex cells) required for sexual reproduction. In meiosis, a dual set of chromosomes (diploid) is diminished to a single set of chromosomes (haploid) to create germ cell or spores. As soon as these combine in sexual reproduction, the result zygote is a diploid. In this way, the chromosomal variety of the types is conserved through sexual reproduction.

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It comes down to chromosomal numbers. If a human, through n = 46 chromosomes, or two pairs the n = 23 chromosomes, were to reproduce there is no chromosomal reduction, the egg cell and also sperm cell would certainly both have actually n = 46 chromosomes. Once these fuse to come to be a gamete, the zygote (embryo) would have n = 92 chromosomes, or double the number necessary! This would result in genetic abnormalities in the child. Further, imagine if this kid were to reproduce with another child v n = 92 chromosomes: their child would have actually 184 chromosomes! This number would certainly be ever-increasing. Thus, a chromosomal reduction is necessary for every species’ continued existence.

Before meiosis begins, the chromosomes in the cell core of the cabinet undergo replication. This is because meiosis produces four daughter cells with half the chromosomes that the parental cell; or 4 haploid cells from a single diploid cell. Remember, haploid and also diploid refer to the number of chromosomes in the cell: haploid cell contain one collection of chromosomes (n) while diploid cells contain two complete sets the chromosomes (2n). As you have the right to see, the mathematics doesn’t quite work-related out: the parental cell must first be convert to a 4n (tetraploid) cabinet before department begins. Therefore a cell v n = 46 chromosomes will be converted to a cell through n = 92 chromosomes, which, ~ meiosis, will develop four cells with n = 23 chromosomes.

Meiosis begins much the exact same as mitosis does. After ~ chromosomal replication, all chromosomes separate right into sister chromatids (the identical two halves that a chromosome). However, below the similarity end. In meiosis, an additional procedure occurs: that of recombination or crossing over. In recombination, the bag of chromosomes heat up and also recombine, so that each chromosome has actually a piece of one more in it. In this way, hereditary diversity is ensured.

Thus, meiosis provides recombination to develop four haploid daughter cell which room not the same to your diploid parent cell or each other.

The Phases that Meiosis

Meiosis is split into 2 parts, or divisions, each of which is composed of numerous phases. These space prophase I, metaphase I, anaphase I and telophase i in meiosis I; and also prophase II, metaphase II, anaphase II and also telophase II in meiosis II. Girlfriend will require some hatchet to know these phases:

Bivalent – a pair the homologous chromosomes hosted together by a chiasma.Chiasma – point of crossing over as soon as chromosomes exchange genetic material.Centromere – the point of constriction of a chromosome.Dyad – fifty percent of a tetrad; one fifty percent of a synapsed pair the homologous chromosomes.Homologous chromosomes – the pair that chromosomes formed by an initial chromosome and its duplication. These chromosomes space not identical.Metaphase plate – the midline that the cell.Monad – after separation, every chromosome that a tetrad forms a monad. A dyad there is no the synapsis come its homologous chromosome.Nuclear envelope – the twin membrane which encloses the nucleus.Nucleolus – the center of rRNA production within the nucleus.Sister chromatids – the two similar chromatids which kind a chromosome.Spindle fibers – a bundle the microtubules running from one pole that the cabinet to another, along which chromosomes move.Synapse/synapsis – the procedure whereby 2 homologous chromosomes come into physical call with one another.Tetrad – a pair the homologous chromosomes hosted together by a chiasma.

Meiosis I

Here is a full snapshot of meiosis i (figure 1), we will certainly go with each step in detail. You should have the ability to understand the far-reaching of every phase and the factor for each step. Once you recognize this, you will be prepared for comment examination questions around meiosis I.


Image Source: Wikimedia Commons

Figure 1: The 4 stages the meiosis I through the prophase stage further separated into four sub-phases

1. Prophase I

Prophase i is characterized by three key events: the condensation of chromatin into visible chromosomes, the synapsis the chromosomes in each homologous pair, and crossing over of hereditary material in between these synapsed chromosomes. Prophase i is further subdivided into five discrete phases: leptonema, zygonema, pachynema, diplonema and also diakinesis (figure 2).


Image Source: Wikimedia Commons

Figure 2: The different stages the the prophase of meiosis I


Also recognized as the leptotene stage, this step is defined by the condensation of chromatin to form visible chromosomes. The homology search begins.


This phase is additionally known together the zygotene stage. The homology search continues, v homologous chromosomes aligning right into rough pairing, forming bivalents. The synaptonemal complex begins to form.


Also well-known as the pachytene stage, this phase has further advance of the synaptonemal complex between homologous bag of bivalents, bring about synapsis. At this phase, it is clear that each bivalent consists of two bag of sisters chromatids. The sisters chromatids of one pair space nonsister chromatids come the sisters chromatids the the various other pair. Together, the four chromatids are well-known as a tetrad. Crossing end or recombination of genetic material in between pairs the nonsister chromatids occurs.


This step is also known as the diplotene stage. The bag of sister chromatids start to separate. Nonsister chromatids continue to be in call at points recognized as chiasmata (singular chiasma), wherein the hereditary exchange has developed during crossing over.


Chromosomes different further however are tho attached v chiasmata that the nonsister chromatids. Separation leads to the chiasmata relocating towards the end of the chromatids, a procedure known together terminalization. The nuclear envelope and nucleolus deteriorate, and the centromeres of every chromosome affix to spindle fibers, before lining increase on the metaphase plate. The chromosomes room still in pairs, which kind tetrads.

2. Metaphase I

This phase is comparable to the metaphase that mitosis. The spindle yarn attached come the centromere of every tetrad align the chromosomes so the one fifty percent of every tetrad is oriented in the direction of each pole.


Image Source: Wikimedia Commons

Figure 3: The alignment the tetrads throughout metaphase i of meiosis I

3. Anaphase I

At anaphase I, the chromosomes perform not separation into your sister chromatids, yet each tetrad is separation into that chromosome bag (dyads). These space pulled to opposite poles in a process known as disjunction. Anaphase ends with the same number of dyads at each pole together the haploid variety of the parent cell.


Image Source: Wikimedia Commons

Figure 4: The splitting of chromosome dyads throughout anaphase I

4. Telophase I

In some organisms, telophase ns is entered and a nuclear membrane forms about the dyads at every pole, prior to a short interphase period is reached. In other organisms, telophase i is skipped, and meiosis II is entered.


Image Source: Wikimedia Commons

Figure 5: formation of nuclear membrane isolating the two dyads

Meiosis II

Once again, us will discover the 2nd meiosis phase lot like the very first one. Right here is a full snapshot of meiosis II following telophase I:


Image Source: Wikimedia Commons

Figure 6: The 4 stages of meiosis II, with 4 haploid cells at the end of this phase

1. Prophase II

Sister chromatids kind dyads connected by a centromere. This are located at the facility of the cell. No condensation the chromatic product or dissolve of atom membranes need occur.


Image Source: Wikimedia Commons

Figure 7: The sister chromatids native the dyads room attached through a centromere during prophase II

2. Metaphase II

Spindle yarn attached to the centromere of every sister chromatid align the dyads in ~ the metaphase plate, with one half of the dyad facing toward every pole.


Image Source: Wikimedia Commons

Figure 8: The metaphase plate develops separating each fifty percent of the dyad

3. Anaphase II

The spindle fibers attached to each sister chromatid shorten, and also each is pulled to an the opposite pole that the cell.


Image Source: Wikimedia Commons

Figure 9: prefer in anaphase I, the sisters chromatids room pulled towards opposite ends

4. Telophase II

The chromatids (monads) are located at the poles the the cell. Cytokinesis occurs, inside a nuclear membrane forms about each set of chromosomes, and also the cell divides into two cells v a haploid variety of chromosomes. Thus, 4 haploid gametes are formed, which can now recombine during sexual reproduction to form a zygote.


Image Source: Wikimedia Commons

Figure 10: four haploid daughter cells type during telophase II

Overview that Meiosis

The details of meiosis deserve to be overwhelming; below we will highlight some key points from both phases the meiosis. During recombination chromosomes native each parental exchange the tips of their homologous chromosomes. This means each homologous chromosome pair has a tiny bit the the various other one. The suggest at i beg your pardon chromosomes exchange product is dubbed a chiasma.


Image Source: Wikimedia Commons

Figure 11: hereditary material exchange during meiosis and the resulting gametes

Why is Meiosis vital in researching Biology?

Meiosis is vital for three main reasons: it enables sexual reproduction the diploid organisms, it permits genetic diversity, and it aids the repair of genetic defects.

1. Enables sexual reproduction the diploid organisms

As discussed previously, meiosis enables the reduction of a diploid cell to a haploid gamete, which deserve to then recombine with another haploid gamete to create a diploid zygote.

2. Enables genetic diversity

The crossing over or recombination of genes which wake up in meiosis rearranges the alleles present in every chromosome that a homologous pair, allowing the mix of paternal and maternal genes, one of two people of which deserve to be express in the resultant offspring. This allows genetic diversity in a population, i beg your pardon is a buffer to hereditary defects, susceptibility the the population to an illness and changes in the environment. Without this recombination, the gene pool of populaces would stagnate, and also a single event might wipe out an entire population. Hereditary diversity method that there will be details individuals within any kind of given populace that will be much better able to endure a ns of habitat, a change in food availability, a change in weather patterns, illness or various other catastrophic events, ensuring varieties continuity.

3. Aids the fix of genetic defects

The recombination which wake up in meiosis have the right to further help in the fix of genetic defects in the following generation. If a hereditary defect is present on a certain allele the one parent, recombination deserve to replace this allele with the healthy allele that the various other parent, permitting healthy offspring.

How is Meiosis various from Mitosis?

Mitosis is the production of 2 genetically similar diploid daughter cell from one diploid parent cell. Meiosis produces 4 genetically unique haploid daughter cells from a solitary diploid parent cell. This germ cells have the right to then incorporate in sex-related reproduction to form a diploid zygote.

Meiosis just occurs in eukaryotic bio organisms i m sorry reproduce sexually, whereas mitosis wake up in all eukaryotic organisms, including those i m sorry reproduce asexually.

The table below summarizes the similarities and also differences in between meiosis and mitosis.



Can only happen in eukaryotes
DNA replication wake up first
Production that daughter cells based on parent cell’s genetic material
Means of cabinet replication in plants, animals, and also fungi


Starts together diploid; ends as haploidStarts as diploid; ends as diploid
Chromosome number is reducedChromosome number is conserved
Chromosome bag undergo synapsisNo synapsis occurs
Used for sex-related reproductionUsed because that growth/healing/asexual reproduction
2 nuclear divisions1 atom division
8 phases5 phases
Daughter cell not identical to parental cellDaughter cell identical to parental cell
Results in 4 daughter cellsResults in 2 daughter cells
Produces germ cellsProduces somatic cells
Occurs just in sexual organismsOccurs in asexual and also sexual organisms

Wrapping up Meiosis and Biology

We now recognize that meiosis is the process of chromosomal reduction which allows the manufacturing of haploid germ cells vital for sexual reproduction. Meiosis is additionally important for its duty in enabling genetic diversity and facilitating the fix of genetic defects with recombination.

The benefits the meiotic reproduction gives over mitotic reproduction are that mitotic reproduction produces the same cells, conserving the chromosomal set and the gene within, vice versa, meiosis enables for the expression of brand-new traits due to the fact that of the process of cross over. There is no meiosis maintaining genetic diversity in ~ populations, organisms would certainly not be able to adapt to suit their environment, nor evolve, nor survive catastrophic events. A population’s genetic diversity is its many reliable device in the fight for the species’ survival.

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