Attention:This post was written a couple of years ago and might not reflect the latest alters in the AP® program. We are gradually updating these posts and also will remove this disclaimer once this write-up is updated. Give thanks to you for her patience!

The word meiosis originates from the Greek language. It method to lessen; this refers to the lessening of the variety of chromosomes within the cell. Meiosis is the process of chromosomal reduction in eukaryotic bio cells (plants, animals, and also fungi), which leader to the production of germ cells (gametes/sex cells) required for sexual reproduction. In meiosis, a twin set the chromosomes (diploid) is decreased to a single set of chromosomes (haploid) to develop germ cells or spores. When these incorporate in sex-related reproduction, the result zygote is a diploid. In this way, the chromosomal variety of the varieties is conserved through sexual reproduction.

You are watching: What is the purpose of meiosis


It comes down to chromosomal numbers. If a human, through n = 46 chromosomes, or 2 pairs that n = 23 chromosomes, were to reproduce without chromosomal reduction, the egg cell and sperm cell would certainly both have n = 46 chromosomes. As soon as these fuse to become a gamete, the zygote (embryo) would have n = 92 chromosomes, or double the number necessary! This would an outcome in genetic abnormalities in the child. Further, imagine if this boy were to reproduce with another child v n = 92 chromosomes: their boy would have 184 chromosomes! This number would be ever-increasing. Thus, a chromosomal reduction is vital for every species’ ongoing existence.

Before meiosis begins, the chromosomes in the nucleus of the cell undergo replication. This is since meiosis produces 4 daughter cell with half the chromosomes the the parent cell; or four haploid cells from a solitary diploid cell. Remember, haploid and diploid refer to the number of chromosomes in the cell: haploid cell contain one collection of chromosomes (n) if diploid cell contain two complete sets that chromosomes (2n). As you deserve to see, the mathematics doesn’t quite job-related out: the parental cell must an initial be converted to a 4n (tetraploid) cell before division begins. So a cell through n = 46 chromosomes will be convert to a cell with n = 92 chromosomes, which, after ~ meiosis, will develop four cells with n = 23 chromosomes.

Meiosis begins much the very same as mitosis does. After ~ chromosomal replication, all chromosomes separate into sister chromatids (the the same two halves the a chromosome). However, here the similarities end. In meiosis, one additional process occurs: the of recombination or crossing over. In recombination, the bag of chromosomes heat up and recombine, so the each chromosome has actually a item of an additional in it. In this way, hereditary diversity is ensured.

Thus, meiosis uses recombination to develop four haploid daughter cells which room not the same to your diploid parental cell or every other.

The Phases of Meiosis

Meiosis is break-up into 2 parts, or divisions, every of which is composed of several phases. These are prophase I, metaphase I, anaphase I and telophase i in meiosis I; and prophase II, metaphase II, anaphase II and telophase II in meiosis II. You will require some terminology to recognize these phases:

Bivalent – a pair of homologous chromosomes organized together by a chiasma.Chiasma – allude of crossing over as soon as chromosomes exchange genetic material.Centromere – the suggest of constriction that a chromosome.Dyad – fifty percent of a tetrad; one fifty percent of a synapsed pair of homologous chromosomes.Homologous chromosomes – the pair that chromosomes created by an initial chromosome and its duplication. This chromosomes space not identical.Metaphase plate – the midline the the cell.Monad – after separation, each chromosome of a tetrad develops a monad. A dyad there is no the synapsis to its homologous chromosome.Nuclear envelope – the twin membrane which encloses the nucleus.Nucleolus – the center of rRNA manufacturing within the nucleus.Sister chromatids – the two the same chromatids which form a chromosome.Spindle fibers – a bundle the microtubules running from one pole of the cabinet to another, along which chromosomes move.Synapse/synapsis – the process whereby 2 homologous chromosomes come right into physical contact with one another.Tetrad – a pair the homologous chromosomes organized together through a chiasma.

Meiosis I

Here is a full photo of meiosis i (figure 1), we will certainly go v each step in detail. Girlfriend should have the ability to understand the significant of each phase and the factor for every step. When you recognize this, you will certainly be prepared for answering examination questions around meiosis I.


Image Source: Wikimedia Commons

Figure 1: The 4 stages of meiosis I v the prophase stage more separated into four sub-phases

1. Prophase I

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


Image Source: Wikimedia Commons

Figure 2: The various stages the the prophase the meiosis I


Also recognized as the leptotene stage, this step is characterized by the condensation of dyed to type visible chromosomes. The homology search begins.


This phase is likewise known as the zygotene stage. The homology search continues, with homologous chromosomes aligning into rough pairing, forming bivalents. The synaptonemal complex starts to form.


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


This phase is additionally known as the diplotene stage. The pairs of sisters chromatids start to separate. Nonsister chromatids stay in call at points known as chiasmata (singular chiasma), whereby the hereditary exchange has developed during cross over.


Chromosomes different further however are quiet attached through chiasmata that the nonsister chromatids. Separation leads to the chiasmata relocating towards the end of the chromatids, a process known as terminalization. The nuclear envelope and nucleolus deteriorate, and also the centromeres of each chromosome connect to spindle fibers, before lining up on the metaphase plate. The chromosomes room still in pairs, which form tetrads.

2. Metaphase I

This step is similar to the metaphase that mitosis. The spindle yarn attached come the centromere of each tetrad align the chromosomes so the one half of every tetrad is oriented in the direction of each pole.


Image Source: Wikimedia Commons

Figure 3: The alignment the tetrads during metaphase ns of meiosis I

3. Anaphase I

At anaphase I, the chromosomes do not break-up into your sister chromatids, however each tetrad is break-up into the chromosome pairs (dyads). These room pulled to opposite poles in a procedure known together disjunction. Anaphase ends through the same variety of dyads at every pole as the haploid number of the parental cell.


Image Source: Wikimedia Commons

Figure 4: The splitting of chromosome dyads throughout anaphase I

4. Telophase I

In part organisms, telophase ns is entered and a atom membrane forms around the dyads at every pole, before a quick interphase period is reached. In other organisms, telophase ns is skipped, and also meiosis II is entered.


Image Source: Wikimedia Commons

Figure 5: formation of nuclear membrane isolating the 2 dyads

Meiosis II

Once again, us will explore the second meiosis phase much like the an initial one. Below is a full photo of meiosis II following telophase I:


Image Source: Wikimedia Commons

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

1. Prophase II

Sister chromatids kind dyads linked by a centromere. This are positioned at the facility of the cell. No condensation the chromatic material or dissolve of nuclear membranes need occur.


Image Source: Wikimedia Commons

Figure 7: The sister chromatids from the dyads are attached by a centromere during prophase II

2. Metaphase II

Spindle yarn attached come the centromere of every sister chromatid align the dyads at the metaphase plate, through one half of the dyad encountering toward each pole.


Image Source: Wikimedia Commons

Figure 8: The metaphase plate forms separating each half of the dyad

3. Anaphase II

The spindle fibers attached to each sister chromatid shorten, and each is pulled to an opposing pole of the cell.


Image Source: Wikimedia Commons

Figure 9: choose in anaphase I, the sister chromatids are pulled in the direction of opposite ends

4. Telophase II

The chromatids (monads) are positioned at the poles of the cell. Cytokinesis occurs, inside a nuclear membrane forms approximately each set of chromosomes, and the cell divides right into two cells through a haploid number of chromosomes. Thus, four haploid gametes are formed, which can now recombine throughout sexual reproduction to type a zygote.


Image Source: Wikimedia Commons

Figure 10: 4 haploid daughter cells kind during telophase II

Overview that Meiosis

The details the meiosis deserve to be overwhelming; below we will certainly highlight some vital points from both phases the meiosis. During recombination chromosomes indigenous each parental exchange the tips of your homologous chromosomes. This way each homologous chromosome pair has a little bit that the other one. The allude at i m sorry chromosomes exchange product is dubbed a chiasma.


Image Source: Wikimedia Commons

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

Why is Meiosis essential in studying Biology?

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

1. Allows sexual reproduction of diploid organisms

As discussed previously, meiosis allows the reduction of a diploid cabinet to a haploid gamete, which can then recombine with one more haploid gamete to create a diploid zygote.

2. Enables hereditary diversity

The crossing end or recombination of genes which wake up in meiosis rearranges the alleles current in every chromosome the a homologous pair, enabling the mixing of paternal and maternal genes, either of which deserve to be express in the resultant offspring. This enables genetic diversity in a population, i beg your pardon is a buffer to hereditary defects, susceptibility the the populace to an illness and changes in the environment. There is no this recombination, the gene swimming pool of populaces would stagnate, and also a single event can wipe out whole population. Hereditary diversity way that there will certainly be details individuals within any given population that will certainly be better able to make it through a loss of habitat, a change in food availability, a adjust in weather patterns, conditions or various other catastrophic events, ensuring types continuity.

3. Aids the fix of genetic defects

The recombination which occurs in meiosis can further assist in the fix of genetic defects in the next generation. If a genetic defect is present on a details allele of one parent, recombination deserve to replace this allele with the healthy allele of the other parent, enabling healthy offspring.

How is Meiosis different from Mitosis?

Mitosis is the production of 2 genetically identical diploid daughter cells from one diploid parent cell. Meiosis produces four genetically distinctive haploid daughter cells from a single diploid parent cell. This germ cells deserve to then incorporate in sexual reproduction to form a diploid zygote.

Meiosis just occurs in eukaryotic bio organisms which reproduce sexually, vice versa, mitosis wake up in all eukaryotic bio organisms, consisting of those i m sorry reproduce asexually.

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



Can only take place in eukaryotes
DNA replication wake up first
Production of daughter cells based on parent cell’s hereditary material
Means of cabinet replication in plants, animals, and fungi


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

Wrapping up Meiosis and Biology

We now understand that meiosis is the procedure of chromosomal palliation which allows the manufacturing of haploid germ cells essential for sex-related reproduction. Meiosis is additionally important because that its duty in allowing genetic diversity and also facilitating the repair of genetic defects through recombination.

The benefits that meiotic reproduction provides over mitotic reproduction are that mitotic reproduction produces similar cells, conserving the chromosomal collection and the gene within, conversely, meiosis enables for the expression of brand-new traits since of the procedure of crossing over. Without meiosis maintaining hereditary diversity in ~ populations, organisms would certainly not have the ability to adapt to suit their environment, no one evolve, nor endure catastrophic events. A population’s hereditary diversity is its many reliable device in the fight for the species’ survival.

Let’s put whatever into practice. Shot this Cellular and also Molecular Biology practice question:


Looking for an ext Cellular and also Molecular Biology practice?

Check the end our other posts on Cellular and also Molecular Biology.

You can likewise find thousands of practice questions top top allows you customize your learning experience come target exercise where you require the most help. We’ll provide you daunting practice concerns to assist you accomplish mastery in Cellular and Molecular Biology.

See more: Why Did Shakespeare Move To London Years, Shakespeare'S London Career

Start practicing here.

Are you a teacher or administrator interested in boosting Cellular and also Molecular Biology college student outcomes?