Difficulty: Beginner to Intermediate | Prerequisites: basic understanding of cell structure (nucleus, chromosomes, DNA replication). If you are not comfortable with what a chromosome looks like or what DNA replication does, review those topics first.
Every living organism needs to make new cells, but not every new cell serves the same purpose. Mitosis is the process that produces identical copies of a cell for growth, repair and maintenance. Meiosis is the process that produces sex cells (gametes) with half the original chromosome number, enabling sexual reproduction and genetic diversity. Understanding the differences between these two processes is one of the cornerstones of introductory biology and comes up repeatedly in genetics, developmental biology and evolution.
Mitosis divides one cell into two genetically identical diploid (2n) daughter cells, used for growth and repair. Meiosis divides one cell into four genetically unique haploid (n) daughter cells, used to make sperm and eggs. The key extras in meiosis are crossing over (which shuffles genes) and two rounds of division instead of one.
Mitosis
A type of cell division that produces two genetically identical daughter cells, each with the same chromosome number as the parent cell (diploid). Think of it as photocopying a cell.
Meiosis
A type of cell division that produces four genetically unique daughter cells, each with half the chromosome number of the parent cell (haploid). In simple terms, this is how the body makes sperm and egg cells.
Diploid (2n)
A cell containing two complete sets of chromosomes, one from each parent. In humans, diploid = 46 chromosomes (23 pairs).
Haploid (n)
A cell containing only one set of chromosomes. In humans, haploid = 23 chromosomes. Sperm and egg cells are haploid.
Homologous chromosomes
A matching pair of chromosomes, one inherited from each parent, that carry genes for the same traits at the same positions. Think of them as two editions of the same book.
Sister chromatids
Two identical copies of a single chromosome, joined at the centromere, produced during DNA replication. They are pulled apart during cell division.
Centromere
The region where sister chromatids are held together. This is the attachment point for the spindle fibres that pull chromatids apart.
Crossing over (recombination)
The exchange of genetic material between homologous chromosomes during prophase I of meiosis. This is one of the main sources of genetic variation in sexually reproducing organisms.
Synapsis
The pairing up of homologous chromosomes during prophase I of meiosis. The paired structure is called a tetrad (four chromatids together).
Tetrad (bivalent)
The four-chromatid structure formed when two homologous chromosomes pair up during synapsis. Each homologous chromosome consists of two sister chromatids, so the tetrad has four chromatids total.
Independent assortment
The random orientation of homologous pairs at the metaphase plate during meiosis I, meaning each gamete gets a different combination of maternal and paternal chromosomes.
Metaphase plate
The imaginary plane at the cell's equator where chromosomes line up before being separated.
Mitosis is a single division that takes one diploid parent cell (2n) and produces two diploid daughter cells (2n), each genetically identical to the original.
Prophase
Chromosomes condense and become visible
Each chromosome has already been duplicated during S phase of interphase, so it consists of two sister chromatids joined at the centromere
The nuclear envelope begins to break down
The spindle apparatus starts to form
Metaphase
Chromosomes align individually (single file) at the metaphase plate
Spindle fibres attach to the centromere of each chromosome
This is the stage where chromosomes are most visible under a microscope
Anaphase
Sister chromatids are pulled apart to opposite poles of the cell
Once separated, each chromatid is now considered an individual chromosome
Telophase and cytokinesis
Nuclear envelopes re-form around each set of chromosomes
Chromosomes decondense
The cytoplasm divides (cytokinesis), producing two separate daughter cells
Each daughter cell is diploid (2n) and genetically identical to the parent
Meiosis involves two consecutive divisions, producing four haploid (n) daughter cells from one diploid (2n) parent cell. The first division (meiosis I) is the "reductive" division. The second (meiosis II) resembles mitosis.
Prophase I
Chromosomes condense
Homologous chromosomes pair up (synapsis), forming tetrads
Crossing over occurs: non-sister chromatids of homologous chromosomes exchange segments of DNA
This is where genetic recombination happens, creating new combinations of alleles
Metaphase I
Tetrads (homologous pairs) line up at the metaphase plate
The orientation of each pair is random (independent assortment), which is another source of genetic variation
Contrast with mitosis: in mitosis, individual chromosomes line up single file; in meiosis I, homologous pairs line up together
Anaphase I
Homologous chromosomes are pulled apart to opposite poles
Sister chromatids remain joined at the centromere
This is the step that halves the chromosome number
Telophase I and cytokinesis
Each pole now has one set of chromosomes (haploid number), though each chromosome still consists of two sister chromatids
The cell divides into two haploid daughter cells
No further DNA replication occurs between meiosis I and meiosis II
Meiosis II proceeds much like mitosis, but starts with a haploid cell.
Prophase II
Chromosomes condense again in each of the two daughter cells
Metaphase II
Individual chromosomes line up at the metaphase plate (single file, as in mitosis)
Anaphase II
Sister chromatids are pulled apart to opposite poles
Telophase II and cytokinesis
Four haploid (n) daughter cells result, each genetically unique
In males, all four become sperm; in females, typically one becomes an egg and three become polar bodies
Feature | Mitosis | Meiosis |
|---|---|---|
Number of divisions | 1 | 2 (meiosis I and II) |
Daughter cells produced | 2 | 4 |
Ploidy of daughter cells | Diploid (2n) | Haploid (n) |
Genetic identity | Identical to parent | Genetically unique |
Crossing over | Does not occur | Occurs during prophase I |
Synapsis / tetrad formation | Does not occur | Occurs during prophase I |
Chromosome alignment (first division) | Single file at metaphase plate | Homologous pairs at metaphase plate |
What separates in first division | Sister chromatids | Homologous chromosomes |
Independent assortment | Does not occur | Occurs at metaphase I |
Purpose | Growth, repair, asexual reproduction | Production of gametes (sex cells) |
Where it occurs | Most body (somatic) cells | Gonads (ovaries and testes) |
Chromosome number notation
2n = diploid number (the full set). In humans, 2n = 46.
n = haploid number (half the set). In humans, n = 23.
Genetic variation from independent assortment
The number of possible chromosome combinations in gametes from independent assortment alone is 2^n, where n is the haploid number. For humans (n = 23), that is 2^23 = 8,388,608 possible combinations per parent, before crossing over adds further variation.
Diagram reference
The source diagrams show side-by-side flowcharts of mitosis and meiosis, starting from a diploid parent cell (2n = 4 in the example). Follow the arrows through each stage and note where the processes diverge: prophase I (synapsis and crossing over), metaphase I (paired vs single-file alignment), and anaphase I (homologous chromosomes vs sister chromatids separating).
Mitosis is the basis of how your body heals a wound: skin cells divide by mitosis to replace damaged tissue. Cancer is essentially mitosis gone wrong, where cells divide uncontrollably because the normal checkpoints fail.
Meiosis is the reason siblings from the same parents look different from each other. The combination of crossing over and independent assortment during meiosis means each egg and each sperm carries a unique genetic mix. This genetic diversity is also why sexual reproduction gives populations a better shot at adapting to changing environments.
Students often think mitosis and meiosis both produce haploid cells. They do not. Mitosis produces diploid cells; only meiosis produces haploid cells.
Students confuse what separates during anaphase I vs anaphase II. In anaphase I, homologous chromosomes separate. In anaphase II, sister chromatids separate. The sister chromatids stay together through all of meiosis I.
Students sometimes think crossing over happens in mitosis. It does not. Crossing over is exclusive to prophase I of meiosis.
Students often assume meiosis II is the "important" division because it comes second. Meiosis I is where the chromosome number is halved and where the two key sources of genetic variation occur (crossing over and independent assortment). Meiosis II is mechanically similar to mitosis.
Expect a question asking you to compare what happens at a specific stage in mitosis vs the equivalent stage in meiosis (e.g. "What lines up at the metaphase plate in mitosis vs meiosis I?")
The distinction between homologous chromosomes separating (anaphase I) and sister chromatids separating (anaphase / anaphase II) is tested frequently
Know the ploidy of daughter cells at every exit point: after mitosis (2n), after meiosis I (n, but chromosomes still consist of two sister chromatids), after meiosis II (n, single chromatids)
Be able to explain the two sources of genetic variation in meiosis: crossing over and independent assortment
Questions about chromosome number often use small example numbers (2n = 4 or 2n = 6) to keep the arithmetic manageable
True or false: Mitosis produces four daughter cells. (False. Mitosis produces two.)
True or false: Crossing over occurs during prophase I of meiosis. (True.)
Fill in the blank: After meiosis I, each daughter cell is ______ (diploid/haploid). (Haploid.)
True or false: In meiosis I, sister chromatids separate. (False. Homologous chromosomes separate in meiosis I; sister chromatids separate in meiosis II.)
Fill in the blank: The number of possible chromosome combinations from independent assortment alone is ______. (2^n, where n is the haploid number.)
Q: A cell has a diploid number of 2n = 6. How many chromosomes will be in each daughter cell after mitosis? After meiosis II?
A: After mitosis, each daughter cell has 6 chromosomes (2n = 6). After meiosis II, each daughter cell has 3 chromosomes (n = 3).
Q: At what stage of meiosis does crossing over occur, and why is it significant?
A: Crossing over occurs during prophase I, when homologous chromosomes are paired in synapsis. It is significant because it creates new combinations of alleles on a chromosome, increasing genetic diversity among offspring.
Q: How does independent assortment contribute to genetic variation?
A: During metaphase I, homologous pairs orient randomly at the metaphase plate. Each possible arrangement sends a different mix of maternal and paternal chromosomes to each daughter cell. With n pairs, there are 2^n possible combinations.
Q: Compare what separates during anaphase of mitosis, anaphase I of meiosis, and anaphase II of meiosis.
A: In anaphase of mitosis, sister chromatids separate. In anaphase I of meiosis, homologous chromosomes separate (sister chromatids stay together). In anaphase II of meiosis, sister chromatids separate.
Q: Why does no DNA replication occur between meiosis I and meiosis II?
A: The goal of meiosis is to halve the chromosome number. If DNA replicated again between the two divisions, the final cells would end up diploid rather than haploid, defeating the purpose of the reductive division.
This material connects directly to genetics: meiosis is the mechanism behind Mendel's laws of segregation and independent assortment. When you study inheritance patterns, pedigrees or Punnett squares, the events of meiosis are what make those predictions work.
It also links to cell cycle regulation and cancer biology. The checkpoints that control mitosis (G1, G2, M checkpoints) are the same ones whose failure leads to uncontrolled cell division. Understanding normal mitosis is the foundation for understanding what goes wrong in tumour cells.
In evolution and population genetics, the genetic variation produced by meiosis (crossing over and independent assortment) is the raw material that natural selection acts on.
mitosis, meiosis, cell division, mitosis vs meiosis, mitosis stages, meiosis stages, prophase, metaphase, anaphase, telophase, prophase I, metaphase I, anaphase I, telophase I, meiosis I, meiosis II, diploid, haploid, 2n, n, homologous chromosomes, sister chromatids, centromere, crossing over, recombination, synapsis, tetrad, bivalent, independent assortment, random assortment, gametes, sex cells, sperm, egg, oocyte, genetic variation, genetic diversity, somatic cells, cytokinesis, spindle fibres, metaphase plate, ploidy, reductive division, equational division, intro to biology, cell biology