Mitosis and Meiosis Simulator
Equations in this simulation
| 2n | diploid number of chromosomes | one set from each parent; 46 in human body cells (n = 23) | |
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| chromatids | copies per chromosome | each chromosome is copied in the S phase before division, so it enters mitosis as two sister chromatids joined at the centromere and each daughter gets one of each |
With the current values:
| n | Chromosome pairs (n; the cell has 2n chromosomes) | meiosis I separates the homologous chromosomes, meiosis II the sister chromatids, giving four haploid cells |
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With the current values:
| C | amount of DNA in one set of chromosomes | doubled by replication, halved at each division |
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With the current values:
| 2ⁿ | ways the homolog pairs can line up in metaphase I | independent assortment: each pair faces either pole by chance; 2²³ = 8.4 million for humans, before crossing over adds more |
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With the current values:
| aneuploid | a cell with a chromosome too many or too few | when a pair (meiosis I) or two sisters (mitosis) go to the same pole; trisomy 21 usually starts this way |
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With the current values:
How to use the mitosis and meiosis simulator
- Choose mitosis or meiosis and the number of chromosome pairs. Red chromosomes came from one parent, blue from the other; pairs of the same size are homologs. The division plays through each phase with its name under the picture: chromatin condensing into X-shaped chromosomes, the nuclear envelope breaking up, the spindle catching them, the line-up and the separation.
- In meiosis watch prophase I: homologs pair up and swap the tips of two chromatids, the crossing over, at the point set by the slider. In metaphase I each pair faces a pole at random, so pressing Reset gives a different combination each time. After two divisions there are four cells, each with one of every pair.
- Tick nondisjunction to make the first pair fail to separate, and see cells end up with a chromosome too many or too few. The chart follows the DNA per cell, 4C before division down to 2C or 1C. For how alleles are passed on, use the Punnett Square Calculator.
Frequently asked questions
What is the difference between mitosis and meiosis?
Mitosis makes two cells genetically identical to the parent, each with the full diploid set (2n); it is how the body grows and repairs. Meiosis makes four haploid cells (n) for sexual reproduction, each with one chromosome of every pair, in two divisions: the first separates homologous chromosomes, the second separates sister chromatids. Crossing over and independent assortment make every product different.
What are sister chromatids and homologous chromosomes?
Sister chromatids are the two identical copies of one chromosome made when the DNA is replicated, joined at the centromere until anaphase. Homologous chromosomes are the two versions of the same chromosome, one from each parent: the same genes in the same order, but possibly different alleles.
What is crossing over?
During prophase I, homologous chromosomes pair up and exchange matching stretches of DNA between non-sister chromatids, at points called chiasmata. The chromatids that come out are new mixtures of the two parents' versions, which shuffles alleles that lie on the same chromosome. Each human chromosome pair crosses over one to three times on average.
What is nondisjunction?
A failure of chromosomes to separate: homologs in meiosis I or sisters in meiosis II or mitosis go to the same pole. One cell gets an extra chromosome and another is missing one. A sex cell with an extra chromosome 21 can produce Down syndrome (trisomy 21); most other trisomies and monosomies are not survivable.
It says WebGL is turned off.
The 3D view needs WebGL, which every current browser has. It can be switched off by hardware acceleration being disabled in the browser settings, or by a very old graphics driver. Turn hardware acceleration on, or try another browser.
Is anything uploaded?
No. The simulation is drawn by your own browser with WebGL; nothing is sent anywhere, and it keeps working offline once the page has loaded.