Meiosis
Biology: Edexcel IGCSE, topic 4.2.2
Meiosis and Mitosis
Sexual reproduction is the fusion (joining together) of male and female gametes. Cells in reproductive organs divide by meiosis to create gametes. Gametes contain half of the number of chromosomes found in all body cells.
Cells split
- Each cell has two sets of chromosomes (they are diploid cells). The chromosomes then replicate and the cell splits in two.
Further cell splitting
- There are now two identical cells.
- The diploid cell divides again.
Haploid cells created
- This creates four genetically different gametes that each have half the number of chromosomes of the parent cell.
- Cells that have only one copy of each chromosome (such as gametes) are called haploid cells, and in humans haploid cells have 23 chromosomes.
Gametes fertilise
- During sexual reproduction, the male gamete fertilises the female gamete and the fertilised cell now has the normal number of chromosomes (46 in humans).
- The random pairing of a male gamete with a female gamete (random fertilisation) creates variation in the offspring because all gametes are genetically different.
Mitosis
- Once the gametes have combined, the new cell divides by mitosis (the cell grows asexually).
- As soon as the embryo reaches a certain size, cells begin to differentiate (specialise).
Test yourself on Meiosis
Meiosis
What are the 4 genetically different gametes produced during sexual reproduction called?