Mitosis and Meiosis

Mitosis

• Mitosis takes place everywhere in the body when:
  • an organism grows
  • damage, such as a cut, is being repaired
  • old or worn-out cells are replaced
  
  
  
• Human cells have chromosomes, this is the number.
  
  
• New cells are identical of the orginal cell.

During Mitosis the following can be observed:
1. chromosomes coil up
2. spindle forms
3. chromosomes arrange along equator (of spindle)
4. one chromatid from each chromosomes pulled to poles
5. chromosomes uncoil nuclear membrane reforms
6. cytokinesis/cell divides into two new cells

Meiosis

• Meiosis takes place in organs.
  
  
• It makes the sex cells ()
  
  
• Each sex cell (sperm or eggs) has the number of chromosomes and so is called a . Human sex cells only have chromosomes.
  
  
• Meiosis involves two divisions. The first one makes a copy of the cells. The second division results in new cells.
• This means that when an egg and a sperm join together through the new cell has chromosomes.
• When the chromosomes are copied, genes can crossover and so forming a new chromosome
• The four daughter cells are not genetically identical. This can gives rise to variation between siblings and even non-identical twins.