Mitosis vs Meiosis
Both divide a cell, and that is where the similarity ends. Mitosis makes two identical copies for growth and repair. Meiosis makes four genetically varied cells with half the chromosome number, for reproduction.
The core differences
- Divisions: mitosis has one, meiosis has two.
- Daughter cells: mitosis makes 2, meiosis makes 4.
- Chromosome number: mitosis keeps it the same, meiosis halves it.
- Genetics: mitosis produces identical cells, meiosis produces varied ones.
- Purpose: mitosis for growth and repair, meiosis for gametes.
Where the variation comes from
- Crossing over in prophase I, where homologous chromosomes swap segments.
- Independent assortment in metaphase I, where each pair lines up independently of the others.
- Random fertilisation afterwards, which is not part of meiosis but multiplies the variation again.
Diploid and haploid
Diploid cells carry chromosomes in pairs, written 2n. Haploid cells carry one of each, written n. Human body cells are diploid with 46 chromosomes; human gametes are haploid with 23. Fertilisation restores 46, which is precisely why gametes must be halved first.
Worked examples
Example 1
Question
A human cell with 46 chromosomes divides. Compare the products of mitosis and meiosis.
Answer
Mitosis: 2 cells with 46 each. Meiosis: 4 cells with 23 each.
Steps
- 1Mitosis copies the DNA once and divides once, so each daughter cell keeps the full 46.
- 2The two products are genetically identical to the parent, barring mutation.
- 3Meiosis copies the DNA once but divides twice, so the number halves.
- 4Each of the four products carries 23 chromosomes, one from each original pair.
- 5Those four are genetically different from each other because of crossing over and independent assortment.
Example 2
Question
A cell with 12 chromosomes completes meiosis. How many cells result, and with how many chromosomes each?
Answer
Four cells with 6 chromosomes each
Steps
- 1The starting cell is diploid with 12, meaning 6 homologous pairs.
- 2Meiosis I separates the pairs, giving two cells with 6 chromosomes each.
- 3Meiosis II separates the sister chromatids without changing the chromosome count.
- 4The result is four haploid cells, each with 6 chromosomes.
It is meiosis I that halves the number, not meiosis II. Meiosis II is mechanically much closer to mitosis.
Example 3
Question
Which process repairs a cut on your skin, and why not the other one?
Answer
Mitosis, because repair needs identical cells with the full chromosome set.
Steps
- 1Repair means replacing skin cells with more skin cells.
- 2The replacements must carry the full diploid genome to function normally.
- 3Mitosis produces genetically identical diploid cells, which is exactly that.
- 4Meiosis would produce haploid, varied cells, which cannot function as body cells.
- 5So all growth and repair in the body is mitosis; meiosis happens only in gamete production.
Common mistakes
Saying meiosis halves the chromosome number because the DNA is not copied.
The DNA is copied once, exactly as in mitosis. The halving comes from dividing twice after a single copy.
Placing crossing over in meiosis II.
It happens in prophase I, while homologous pairs are together. They have already separated by meiosis II.
Describing the four products of meiosis as identical.
They are genetically different. Producing variation is the point of the process.
Saying mitosis produces gametes.
Gametes come from meiosis. Mitosis handles growth, repair, and asexual reproduction.
Practice it
Work these out first, then open the answer. Stuck halfway? Select the problem and ask Solvecoon for the step you are missing.
1. Which process produces gametes?
Show answer
Meiosis, because gametes must be haploid and varied.
2. A cell with 20 chromosomes undergoes mitosis. What do the daughter cells contain?
Show answer
Two cells, each with 20 chromosomes, genetically identical to the parent.
3. Name two sources of genetic variation in meiosis.
Show answer
Crossing over in prophase I and independent assortment in metaphase I.
Questions people ask
- Is meiosis II the same as mitosis?
- Mechanically it is very similar, separating sister chromatids. The difference is that it starts with haploid cells, so the products stay haploid.
- Where does meiosis happen in humans?
- In the testes and the ovaries, producing sperm and egg cells. Every other dividing cell in the body uses mitosis.
- How many chromosomes does a human gamete have?
- 23, one from each homologous pair. Fertilisation combines two gametes to restore 46.
- What is the easiest way to remember which is which?
- Mitosis makes more of the same. Meiosis makes half, and makes them different.
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