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💡 Halving to keep the balance
If both parents gave a full set of chromosomes, every generation would carry double. Meiosis solves this by handing each gamete exactly half.
What is meiosis?
- A special type of cell division that forms gametes .
- It reduces the chromosome number of a parent cell ( diploid ) to half ( haploid ) in the daughter cells.
- Humans have 23 pairs (46 chromosomes); each human gamete carries only 23 .
What are gametes?
- The haploid cells used only for reproduction are called gametes .
- In animals, the male gamete is sperm and the female gamete is the egg .
- In plants, the pollen grain carries the male gametes and delivers them to the ovule , which contains the female gamete (egg).
In this Activity, we will explore how meiosis creates variation by making combinations from three pairs of coloured beads.
- Take three pairs of beads of different colours, each pair standing for two contrasting characters (Fig. 11.9).
- Pair 1 (green): blonde vs black hair; Pair 2 (blue): straight vs curly hair; Pair 3 (red): brown vs black eyes.
- Make a combination by randomly picking one bead from each pair.
- Write your combination, e.g. ‘light green, light blue, light red’.
- Count how many combinations are possible — with three pairs, eight combinations arise; imagine the number with 23 pairs.
What we observe
Just three pairs give
eight
different combinations — showing how meiosis produces enormous variation, making each child genetically unique.
How does meiosis create variation?
- During meiosis, the chromosomes of each pair separate randomly into the gametes.
- Each gamete receives a unique mix of characters from the many chromosomes.
- Fusion of two such gametes makes children genetically different from their parents and from their siblings — variation that helps species adapt and evolve.
Mitosis vs Meiosis
Mitosis
Meiosis
Produces body cells and asexual offspring
Produces gametes for sexual reproduction
Chromosome number stays the same
Chromosome number is halved
Daughter cells are identical to the parent
Gametes carry a unique mix (variation)
