Cell Division

• Found in the nucleus of animal and plant cells
• Made up of really long molecules called chromosomes

• A gene is a section of DNA, it contains the instructions to make specific protein
• Cells make proteins by stringing amino acids together in a certain order
• DNA determines what proteins the cell produces which in turn determines what type of cell it is, e.g. haemoglobin --> red blood cell 

Mitosis makes new cells for growth and repair and it is when a cell reproduces itself by splitting to form two identical offspring

• Body cells have two copies of each chromosome (one from the mother and one from the father)
• Human body cells have 46 chromosomes and gametes have 23 so when the male & female gamete combine you get 46 chromosomes again

• DNA is copied and forms X-shaped chromosomes each 'arm' the exact copy of the other
• Chromosomes then line up in the middle of the cell and cell fibres pull them apart
• Membrane forms around each set of chromosomes, these become the nuclei of the two new cells
• Then the cytoplasm divides and two new identical cells are formed

Asexual reproduction also uses mitosis, the offspring have no variation because they have the same genes. 

Meiosis produces cells with only half the normal number of chromosomes

• As with mitosis ty DNA duplicates and in the first division the chromosomes pairs are lined up in the centre of the cell
• The pairs are pulled apart so each new cell only has one copy of each chromosome
• Each new cell has a mixture of the mother's and the father's chromosomes, this creates variation on the offspring
• In the second division the chromosomes line up again and the arms are pulled apart 
• Now you get four gametes with only a single set of chromosomes in it