Chromosomes and Mitosis

• Most cells in your body have a nucleus. The nucleus contains your genetic material in the form of chromosomes.
• Chromosome are coiled up lengths of DNA molecules.
• Each chromosome carries a large number of genes. Different genes control the development of different characteristic, e.g. hair colour.
• Body cells normally have two copies of each chromosomes - one from the organism‘s ’mother’, and one from it‘s ‘father’. So, humans have two copies of chromosome 1, two copies of chromosome 2, etc.
• Body cells in multicellular organisms divide to produce new cells as part of a series of stages called the cell cycle.
• The stage of the cell cycle when the cell divides is called mitosis. Multicellular organisms use mitosis to grow or replace cells that have been damaged.
• The end of the cell cycle results in two new cells identical to the original cell, with the same number of chromosomes.
• The two main stages of the cell cycles are: growth and DNA replication, and mitosis.
• During the cell cycle, growth and DNA replication happens. This is where, in a cell that’s not dividing, the DNA is spread out in long strings. Before it divides, the cell has to grow and increase the amount of subcellular structures such as mitochondria and ribosomes. It then duplicates its DNA is copies and forms X-shaped chromosomes. Each ‘arm’ of the chromosome is an exact duplicate of the other.
• During the cell cycle, once the cells contents and DNA have been copied, the cell is ready for mitosis. This is where the chromosomes line up at the centre of the cell and cell fibres pull them apart. The two arms of each chromosomes go to opposite ends of the cell. Membranes form around each of the sets of chromosome. These become the nuclei of the two new cells - the nucleus has divided. Lastly, the cytoplasm and cell membrane divide.
• Once mitosis has happened in the cell cycle, the cell has now produced two new daughter cells. The daughter cells contain exactly the same DNA - they’re identical. Their DNA is also identical to the parent cell.