biology 1.3

• Cells use the process of DNA replication prior to cell division to make an identical copy of their DNA. Each daughter cell formed receives a full complement of DNA which is identical to the parent cell.
• Binary fission in prokaryotic cells

  1. Circular chromosome replicates

  2. Chromosome attaches to cell membrane

  3. Cell divides into two new cells
• Mitosis in eukaryotic cells

  1. Division of the nucleus (mitosis)

  2. Division of the cytoplasm (cytokinesis)
• Mitosis


  • Consists of four phases: Prophase, Metaphase, Anaphase, Telophase
• Prophase


  1. Nuclear membrane breaks down

  2. Chromosomes condense and become visible

  3. Each chromosome consists of a pair of identical chromatids joined by a centromere

  4. Spindle fibres assemble to form the spindle
• Metaphase


  Pairs of chromatids are moved to the equator of the spindle by the spindle fibres
• Anaphase


  1. Chromatid pairs are separated to form two identical sets of daughter chromosomes

  2. Daughter chromosome sets are moved to the poles of the spindle by the spindle fibres
• Telophase


  1. Spindle breaks down

  2. Chromosomes de-condense and become enclosed by a nuclear membrane
• Chromosomes in eukaryotic cells are linear
• Prokaryotic cells divide by binary fission
• Eukaryotic cells divide by mitotic division
• Sperm and ova are haploid cells, carrying one chromosome from each homologous pair
• Somatic cells in humans are diploid, carrying 23 pairs of homologous chromosomes
• Karyotyping involves photographing and arranging the different chromosomes into numbered homologous pairs
• Cancer can result from uncontrolled cell division, forming tumours