Cell Division: Mitosis and Meiosis (Stages, Differences, and How to Remember Them)

A cut on your skin heals. A child grows into an adult. A single fertilized egg becomes a whole body. All of this happens because cells can divide, copying themselves to build, grow, and repair. Cell division is the process by which one parent cell splits into two or more daughter cells.

Cells divide in two different ways, for two different reasons. Mitosis makes exact copies for growth and repair. Meiosis makes gametes (eggs and sperm) for reproduction. This article walks through the stages of each, sets them side by side so the differences are clear, and gives you simple ways to remember the order.

The general steps of cell division are karyokinesis (a division of the nucleus) and cytokinesis (a division of cytoplasm). The karyokinesis stage of mitosis has two primary phases: interphase and M phase. The M phase is where cell division begins and has four steps: prophase, metaphase, anaphase, and telophase.

Meiosis has two divisions: meiosis I and meiosis II. Meiosis II follows meiosis I without any DNA copying in between. Each division has the same four stages seen in mitosis: prophase, metaphase, anaphase, and telophase.

Figure: Mitosis VS Meiosis

Mitosis Cell Division

Mitosis is a process of the cell cycle that occurs in plant and animal cells where the division of pre-existing cells produces two identical daughter cells. During mitosis, replicated chromosomes are separated into two daughter nuclei containing equal amounts of genetic information. On account of this, mitosis is also known as equational cell division.

Figure: Stages of Mitosis Cell Division

Stages of Mitosis Cell Division

Howard and Pele (1953) have divided the cell cycle into G1, S, G2, and M phases. G1 phase, S phase, and G2 phase are combined in the interphase.

Interphase

It is the prolonged cell cycle phase where the daughter cell prepares before the mitosis phase begins. It is divided into three stages;

G1 phase

• This phase is also known as the first gap phase or first growth phase. It is not a resting phase. The cell is very active, growing in size and making the proteins and organelles it will need.
• DNA synthesis does not take place yet.
• It involves the synthesis of RNA, protein, and membranes needed for the development of cytoplasm and nucleus of daughter cells.

S phase

• Also known as S-phase or synthetic phase
• It involves the synthesis of histone protein (needed for replication), and two DNA molecules are formed by replication.

G2 phase

• Also known as the second gap phase or second growth phase
• The phase where DNA synthesis ends and the prophase stage initiates
• Continuous synthesis of RNA and proteins that is required for cell growth takes place.

Mitotic phase or M-phase

It is the short period of chromosome condensation, separation, and cytoplasmic division. It begins as soon as the G2 phase ends. It is divided into the following phases:

Prophase(Pro= Before; Phasis= Appearance)

• The appearance of a thin-thread-like condensing chromosome containing two chromatids held together by the centromere marks the first phase of mitosis, called prophase.
• The cell begins the process of division.
• The nuclear envelope disappears.
• Formation of the spindle or mitotic apparatus in the cytoplasm takes place.

Prometaphase:

• The nuclear envelope’s disappearance marks the prometaphase’s initiation and enables the mitotic spindle to interact with the chromosome.
• The spindle fibers begin moving the chromosomes toward the center of the cell, the metaphase plate. This movement is the characteristic feature of the stage.
• Microtubules attach to the kinetochore; balanced bipolar force holds the chromosomes on the metaphasic plate.

Metaphase

• Chromosomes are the shortest and thickest.
• Centromeres occupy the plane of the equator of the mitotic apparatus (equatorial or metaphasic plate)

Anaphase

• It begins rapidly with the synchronous splitting of each chromosome into its sister chromatids, called daughter chromosomes. Each daughter chromosome carries its own kinetochore.
• After separation, each chromosome moves toward the opposite pole. As the microtubules of the mitotic spindle pull chromosomes, they appear V-shaped.

Telophase

• The end of the polar migration of daughter chromosomes marks the beginning of the telophase.
• Each separated daughter chromosome resumes their long, slender, extended form as their coils relax
• Nuclear envelopes reunify around each group of chromosomes to form daughter nuclei.
• Mitotic apparatus except the centrioles disappears.
• Telophase is followed by cytokinesis, constricting the cytoplasm into two separate cells.

Purpose/Significance of mitosis

1. To maintain proper size of the cell
2. To maintain equilibrium in quantity of RNA and DNA  in the cell
3. To restore old or dead cells of the body
4. In some organisms, it is involved in asexual reproduction
5. Provides opportunity for the growth or development of organs and the body of individuals
6. Maintains equal distribution of chromosome to each daughter cell with pure genome as recombination or crossing over does not take place in mitosis.
7. Embryogenesis and blastogenesis both involves mitosis
8. Germ cells in the gonads first multiply their numbers by mitosis. The actual gametes (eggs and sperm), however, are made by meiosis, not mitosis.

Meiosis Cell Division

Van Beneden first described meiosis cell division in 1883. Meiosis is defined as the process of cell division in which the original diploid cell divides twice to produce a total of four haploid cells. Thus, formed haploid cells consisting of half number of chromosome as the original diploid cell gives rise to gametes (sperm or eggs) that, on fertilization, supports sexual reproduction and a new generation of a diploid organism.

Figure: Stages of Meiosis Cell Division

Stages of meiosis cell division

Meiosis is one round of DNA copying followed by two divisions. This gives it the following parts: pre-meiotic interphase (DNA is copied once), meiosis I (the reduction division, where the chromosome number is halved), a short interkinesis, and meiosis II (which separates the sister chromatids, like mitosis). The key point: DNA is copied once but the cell divides twice, which is why four cells result, each with half the chromosomes.

Pre-meiotic interphase

• Before entering into meiosis I, a cell undergoes a period of growth phase called interphase
• DNA duplication occurs at the S-phase.
• The nucleus and nucleolus become visible.

Meiosis I

It is also known as reductive division or heterotypic division, because the chromosome number is reduced from diploid (2n) to haploid (n). The two cells produced are haploid. Meiosis I has the same four stages as mitosis, prophase I, metaphase I, anaphase I, and telophase I, but prophase I is far longer and more complex, and it is where crossing over happens.

Prophase I

It is the longest phase, taking up to 90% of meiosis I, with sub-stages usually listed as: leptotene, zygotene, pachytene, diplotene, and diakinesis. (Some textbooks add an early proleptotene step.)

1. Leptotene or Leptonema: Chromosome becomes more uncoiled and long thread-like structure with a specific orientation inside the nucleus that looks like a ball of knitting wool. After duplication of centrioles, each pole of the cell possesses two centrioles. The process of homology search begins to initiate the pairing of homologs.
2. Zygotene or Zygonema: The two homologous chromosomes in each pair, one inherited from the mother and one from the father, come together. This pairing is known as synapsis. The pairing of homologous chromosomes is exact and specific (gene-for-gene). A protein-containing framework, Synaptonemal Complex (SC), joins the paired homologous chromosomes till crossing over completes.
3. Pachytene or Pachynema: The synapsed pair becomes thick and short. Because it contains two homologous chromosomes and four chromatids in total, it is called a bivalent (or tetrad). The crucial genetic phenomenon “Crossing Over” takes place. It is the interchange of chromatin material between one non-sister chromatid of each homologous chromosome accompanied by chiasmata formation. During crossing over, the non-sister chromatids break at matching points and rejoin with the segments swapped. This exchange reshuffles the genes carried on the two chromosomes.
4. Diplotene or Diplonema: Unpairing or desynapsis of homologous chromosomes initiates, and first, chiasmata appear. The synaptonemal complex disappears, but the homologous chromosomes stay physically joined at one or more points called chiasmata. These chiasmata mark where crossing over took place.
5. Diakinesis: The chiasmata slide toward the ends of the chromosomes. This sliding is called terminalization. The homologous chromosomes stay joined at these end points until metaphase I. Chromosomes are now at their most condensed.

As prophase I ends, the nuclear envelope breaks down and the spindle forms between the two poles. The tightly coiled chromosomes then move toward the spindle's equator, leading into metaphase I.

Metaphase I

Spindle fiber attached to the chromosome helps align the chromosome at the equator. This stage terminates as soon as the homologous chromosomes start to separate from each other.

Anaphase I

The homologous chromosome gets separated and moves towards the opposite pole. Actual reduction and disjunction occur at this stage. The number of chromosomes at each pole is precisely half (n) as each pole receives one homologous chromosome from each bivalent present in the cell.

Telophase I

The arrival of a half set of chromosomes at each pole defines the initiation of telophase. Nucleolus reappears. Chromosomes uncoil, and a nuclear envelope is formed around the chromosomes. After Karyokinesis, cytokinesis occurs through which two haploid cells are formed.

Intra Meiotic or Interkinesis

The short phase between telophase I and prophase II. No DNA replication occurs here, which is what makes meiosis different from two rounds of mitosis.

Meiosis II

It is also known as the Equational Division or Homotypic Division. This stage includes dividing each haploid meiotic cell into two haploid cells. It consists of four steps;

Prophase II

• Centrioles duplicate into two and move toward the opposite pole.
• Chromosomes with two chromatids become short and thick.
• The nuclear membrane and nucleolus disappear.

Metaphase II

• Chromosomes line up singly on the equator of the spindle.
• Spindle fibers attach to the two kinetochores of each chromosome from opposite poles.

Anaphase II

• The centromere of each chromosome splits, and the two sister chromatids separate. These daughter chromosomes move toward opposite poles as the spindle microtubules shorten.

Telophase II

• Chromatids migrate to the opposite poles known as chromosomes.
• A nuclear envelope is formed around the chromosome, and the nucleolus reappears.
• After Karyokinesis, cytokinesis occurs in each haploid meiotic cell, resulting in four haploid cells.
• Because of crossing over and the way chromosomes were shuffled in meiosis I, the four cells are all genetically different from one another.

Purpose/Importance of Meiosis

1. Meiosis maintains a persistent number of chromosomes in the organisms.
2. By crossing over, genetic variations among the species can lead to evolution.
3. It also facilitates segregation and an independent assortment of genes.
4. Leads to the continuity of generations by producing gametes(sperm and ova) in sexually reproducing species.

Why two kinds of division exist

If cells only needed to grow and repair, mitosis alone would be enough. The problem is reproduction.

Imagine if eggs and sperm were made by mitosis. Each would carry the full set of 46 chromosomes (in humans). At fertilization, egg plus sperm would give 92. The next generation would have 184, and the number would double forever. Life could not work this way.

Meiosis solves this. It halves the chromosome number, so each gamete carries 23. Egg (23) plus sperm (23) restores the correct 46 at fertilization. The number stays stable generation after generation.

Meiosis does a second job at the same time. Through crossing over and the random mixing of chromosomes, it makes every gamete genetically unique. This is why siblings are not identical. That variation is the raw material for evolution.

So the short answer to "what kind of cell divides by meiosis?" is: only the germ cells that make gametes. Every other cell in your body divides by mitosis.

Mitosis vs meiosis: the key differences

Both start with one cell and involve the same basic machinery, spindles, chromosomes, and the PMAT stages. The differences are in the purpose and the outcome.

The one idea that ties the table together: mitosis copies, meiosis shuffles and halves. Mitosis exists to make more of the same cell. Meiosis exists to make variety and to keep the chromosome number stable across generations.

How to Remember

The order of mitosis phases: IPMAT.
Interphase, Prophase, Metaphase, Anaphase, Telophase. Say it as one word: "IP-MAT." (Some teachers add prometaphase between P and M: I-P-PM-M-A-T.)

What happens in each, in one word:

Metaphase = Middle and Anaphase = Apart are the two that students mix up. Both start differently (M vs A) and mean different things (line up vs pull apart). Lock those two and the rest follows.

Prophase I sub-stages of meiosis: "Lazy Zebras Pick Diet Drinks."
Leptotene, Zygotene, Pachytene, Diplotene, Diakinesis. What happens in each: chromosomes appear (lepto), pair up (zygo, synapsis), crossing over (pachy), chiasmata show (diplo), terminalization (diakinesis).

Reductional vs equational. Meiosis I reduces the number (2n → n), so it is reductional. Meiosis II just splits chromatids like mitosis, so it is equational. Remember: the reduction happens first.

Mitosis vs meiosis, the core split: Mitosis = one division, identical copies. Meiosis has an extra "i" and an extra division: i for the two divisions and the individuality (variation) it creates.

Key exam facts

Which phase is longest / shortest (common exam question):

Why anaphase is shortest: it is only the moment of pulling chromosomes apart, a fast mechanical step, while prophase involves long, complex preparation (condensing, pairing, crossing over).

Where students get confused

Mitosis vs meiosis outcome. Mitosis makes 2 identical diploid cells. Meiosis makes 4 non-identical haploid cells. If you only remember one thing: mitosis copies, meiosis halves and shuffles.

Meiosis I vs meiosis II. Meiosis I separates whole homologous chromosomes and halves the number (this is the reduction). Meiosis II separates sister chromatids, like mitosis, and does not change the number. The reduction is done in meiosis I; meiosis II just tidies up.

Homotypic vs heterotypic division. These are just other names. Heterotypic = meiosis I (homologous pairs separate, number changes). Homotypic = meiosis II (chromatids separate, number stays). Hetero for the one where partners are different and split; homo for the mitosis-like one.

Chromatid vs chromosome vs homologous chromosome. A chromosome is one DNA molecule. After copying, it has two identical sister chromatids joined at the centromere. A homologous chromosome is the matching partner chromosome (one from each parent). Sisters are identical copies; homologs are a matching pair that are similar but not identical.

Crossing over vs independent assortment. Both create variety, but differently. Crossing over swaps pieces between homologous chromosomes during prophase I. Independent assortment is the random way each pair lines up and separates, so different combinations end up in different cells. One shuffles within pairs; the other shuffles between pairs.

Equational vs reductional division. Reductional halves the chromosome number (meiosis I). Equational keeps the number the same (mitosis, and meiosis II). "Reduction" tells you the number went down.

References

1. Urry LA, Cain ML, Wasserman SA, Minorsky PV, Reece JB. Campbell Biology. 12th ed. Pearson; 2021.
2. Alberts B, Heald R, Johnson A, et al. Molecular Biology of the Cell. 7th ed. W. W. Norton; 2022.
3. Lodish H, Berk A, Kaiser CA, et al. Molecular Cell Biology. 9th ed. W. H. Freeman; 2021.
4. Cooper GM. The Cell: A Molecular Approach. 8th ed. Oxford University Press; 2019.
5. National Center for Biotechnology Information. Meiosis. In: Molecular Biology of the Cell. Bookshelf. Available from: https://www.ncbi.nlm.nih.gov/books/NBK26840/