Chromosomes and Mitosis

• Most cells in your body have a nucleus. The nucleus contains your genetic material in the form of chromosomes.
• Chromosomes 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 chromosome - one from the organism’s ‘mother’ and one from its ’father’. So humans have two copies of chromosome 1 and two copies of chromosome 2, etc.
• The diagram shows 23 pairs of chromosomes from a human cell.

  
• Body cells in multicellular organisms divide to produce new cells as part of a series of stages called the cells 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.
• 2) Growth & DNA Replication: Before the cell divides, it has to grow and increase the amount of subcellular structures such as mitochondria and ribosomes.
• 3) Growth & DNA Replication: The cell duplicates its DNA - so there is one copy for each new cell. The DNA is copied and forms X-shape chromosomes. Each ‘arm’ of the chromosome is an exact duplicate of the other.
• 4) Mitosis: The chromosomes line up at the center of the cell and cell fibres pull them apart. The two arms of each chromosome go to opposite ends of the cell.
• 5) Mitosis: Membranes form around each of the sets of chromosome. These become the nuclei of the two new cells, the nucleus has divided.
• 6) Mitosis: Lastly the cytoplasm and cell membranes divide. The cells has now produced two new daughter cells. The daughter cells contains exactly the same DNA - they are identical. Their DNA is also identical to the parent cell.
• Growth & DNA Replication: In a cell that is not dividing, the DNA is spread out in long strings.