Meosis
What Is Meiosis?
Meiosis is a special type of cell division that produces gametes (sperm and egg cells) with half the number of chromosomes.
💡 Key Concept: Meiosis ensures offspring receive the correct number of chromosomes and introduces genetic variation.
Why Is Meiosis Important?
✔ Produces haploid cells (with half the normal number of chromosomes – 23 in humans).
✔ Introduces genetic variation – offspring are genetically different from parents.
✔ Essential for sexual reproduction.
Where Does Meiosis Happen?
Organism | Site of Meiosis |
Humans (male) | Testes – produces sperm |
Humans (female) | Ovaries – produces eggs |
Plants | Anthers (pollen) and ovaries (ovules) |
Stages of Meiosis (Simplified)
1️⃣ Chromosomes are duplicated (copied).
2️⃣ Cells divide twice – first to separate chromosome pairs, then to separate individual chromosomes.
3️⃣ This produces four genetically different haploid cells.
Summary:
Step | What Happens |
Start | One diploid cell (46 chromosomes in humans). |
Division 1 | Chromosome pairs separate. |
Division 2 | Chromosomes split again. |
End | Four haploid gametes (23 chromosomes). Each one is genetically different. |
💡 Difference from mitosis: Mitosis makes 2 identical cells. Meiosis makes 4 non-identical gametes.
How Meiosis Leads to Variation
✔ During meiosis, chromosomes are shuffled and assorted randomly.
✔ This means each gamete contains a unique mix of genes.
✔ At fertilisation, the combination of gametes increases variation further.
Questions
- What does meiosis produce?
- How many cells are made at the end of meiosis?
- Are the cells identical or different?
- Where does meiosis happen in humans?
- Why is meiosis important in reproduction?
Summary
- Meiosis is a type of cell division that produces 4 genetically different haploid gametes.
- It takes place in the reproductive organs.
- Meiosis introduces variation, which is key to natural selection and evolution.
- It is essential for sexual reproduction.