Meiosis
Meiosis makes four genetically different gametes with half the chromosomes.
About this topic
Meiosis is a two-division process producing four genetically different haploid gametes (sperm or eggs), each with half the chromosome number. In meiosis I homologous chromosomes pair, crossing over exchanges segments, and they separate; in meiosis II sister chromatids separate. Independent assortment and crossing over create variation.
Fertilisation restores the diploid number. Errors like nondisjunction cause conditions such as Down's syndrome (trisomy 21). Meiosis underlies sexual reproduction and genetic diversity.
Meiosis halves the chromosome number so that when two gametes fuse at fertilisation, the full number returns. Humans go from 46 chromosomes to 23 in each gamete. Variation comes from two sources: crossing over in prophase I, and independent assortment, where each pair lines up randomly. With 23 pairs, there are over 8 million possible combinations in one person's gametes, before crossing over.
This explains why siblings, apart from identical twins, differ from one another. Errors such as non-disjunction, where chromosomes fail to separate, cause conditions like Down syndrome. A common mistake is mixing up the two divisions: in meiosis I homologous pairs separate, in meiosis II sister chromatids separate, like mitosis. Meiosis happens only in the reproductive organs.
Key ideas
- Two divisions
- Crossing over shuffles alleles
- Produces sperm and eggs
Quick check
Use cases: where Meiosis helps
- Homework: review the key idea behind Meiosis before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Meiosis without notes.
- Visual learning: play with the interactive lab to see how Meiosis changes when you adjust its inputs.
- Teaching a friend: explain Meiosis in your own words, then compare your version with the key ideas.
Biology underpins medicine, farming, conservation and biotechnology.
Frequently asked questions
What is Meiosis?
Meiosis makes four genetically different gametes with half the chromosomes.
What will I learn in Meiosis?
Two divisions. Crossing over shuffles alleles. Produces sperm and eggs.
Is Meiosis part of Biology?
Yes. It is one of 150 Biology topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Meiosis lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Meiosis?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.